Method for csi feedback in wireless communication system, and apparatus therefor

ABSTRACT

A method for feeding back channel state information (CSI) in a wireless communication system, carried out by a terminal, according to the present specification comprises the steps of: transmitting, to a base station, capability information of the terminal for CSI-related action; receiving configuration information for the CSI-related action from the base station; tracking partially activated CSI reference signal (RS); measuring fully activated CSI-RS; and reporting the results of the measurement to the base station.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for feeding back, by a terminal, channelstate information (CSI) based on a reference signal and an apparatus forsupporting the same.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices while ensuring the activity of a user. However, the mobilecommunication systems have been expanded to their regions up to dataservices as well as voice. Today, the shortage of resources is causeddue to an explosive increase of traffic, and more advanced mobilecommunication systems are required due to user's need for higher speedservices.

Requirements for a next-generation mobile communication system basicallyinclude the acceptance of explosive data traffic, a significant increaseof a transfer rate per user, the acceptance of the number ofsignificantly increased connection devices, very low end-to-end latency,and high energy efficiency. To this end, research is carried out onvarious technologies, such as dual connectivity, massive Multiple InputMultiple Output (MIMO), in-band full duplex, Non-Orthogonal MultipleAccess (NOMA), the support of a super wideband, and device networking.

DISCLOSURE Technical Problem

An object of this specification is to provide a method for sending orreceiving capability information of a UE related to a CSI operation.

Furthermore, an object of this specification is to provide a method fortracking a partial activation CSI-RS and performing measurement andreporting on a full activation CSI-RS only so as to reduce latency in aCSI feedback procedure.

Furthermore, an object of this specification is to provide a method forinitializing or updating a CSI measurement-related window.

Technical objects of the present invention are not limited to theaforementioned objects, and those skilled in the art will clearlyunderstand other technological objects not described above from thefollowing description.

Technical Solution

This specification provides a method for performing channel stateinformation (CSI) feedback in a wireless communication system, themethod being performed by a UE and including sending capabilityinformation of the UE for a CSI-related operation to an eNB, receivingCSI-related operation configuration information from the eNB, whereinthe CSI-related operation configuration information includes at leastone of partial activation CSI-related operation index informationindicative of a CSI-related operation of performing partial activationand full activation CSI-related operation index information indicativeof a CSI-related operation of performing full activation, tracking apartial activation CSI-reference signal (RS), measuring a fullactivation CSI-RS, and reporting results of the measurement to the eNB.

Furthermore, in this specification, measuring the full activation CSI-RSincludes receiving a first message indicative of the activation of themeasurement of the full activation CSI-RS from the eNB and measuring thefull activation CSI-RS activated by the first message.

Furthermore, in this specification, the CSI-related operation is relatedto at least one of a CSI-RS, CSI-interference management (IM) and a CSIprocess.

Furthermore, in this specification, the capability information of the UEincludes first control information indicative of a maximum number of theCSI-related operations capable of simultaneously full activation andsecond control information indicative of a maximum number of theCSI-related operations capable of simultaneously partial activation.

Furthermore, in this specification, tracking the partial activationCSI-RS includes performing synchronization with the partial activationCSI-RS in a time and/or frequency.

Furthermore, in this specification, the tracking is performed byapplying a specific reference signal (RS) included in the CSI-relatedoperation configuration information and quasi co-location (QCL)assumption.

Furthermore, in this specification, the full activation CSI-RS isselected from the partial activation CSI-RS.

Furthermore, in this specification, the first message includes a mediaaccess control (MAC) control element (CE) or downlink controlinformation (DCI).

Furthermore, in this specification, the method further includesreceiving third control information related to a CSI-RS measurementwindow from the eNB. Measuring the CSI-RS includes initializing orupdating the CSI-RS measurement window when the first message isreceived, repeatedly performs the measurement of a CSI-RS from a pointof time at which the CSI-RS measurement window is initialized or updatedto a specific period, and averaging the results of the measurement.

Furthermore, in this specification, if the CSI feedback is periodic CSIfeedback, the point of time at which the CSI-RS measurement window isinitialized or updated includes a specific reference resource point oftime related to a rank indicator (RI) report first generated after thespecific period.

Furthermore, in this specification, the first message is received fromthe eNB for each CSI process.

Furthermore, in this specification, the first message includesbeam-change indicator (BCI) signaling providing notification of a changein a beamforming-related matrix.

Furthermore, this specification provides a user equipment for feedingchannel state information (CSI) back in a wireless communication system,the UE including a radio frequency (RF) unit sending or receiving aradio signal and a processor controlling the RF unit. The processorperforms control so that capability information of the UE for aCSI-related operation is transmitted to an eNB, CSI-related operationconfiguration information is received from the eNB, wherein theCSI-related operation configuration information includes at least one ofpartial activation CSI-related operation index information indicative ofa CSI-related operation of performing partial activation and fullactivation CSI-related operation index information indicative of aCSI-related operation of performing full activation, a partialactivation CSI-reference signal (RS) is tracked, a full activationCSI-RS is measured, and results of the measurement are reported to theeNB.

Advantageous Effects

This specification has an advantage in that latency in a CSI feedbackprocedure can be reduced by sending CSI configuration-relatedinformation to a UE in the MAC level or PHY level.

Furthermore, this specification has an advantage in that more accurateCSI feedback can be performed because the past environment is notunnecessarily incorporated into CSI measurement by initializing orupdating a CSI measurement-related window at a point of time at whichthe activation of CSI measurement is indicated or a point of time atwhich a change of a CSI configuration is notified.

Advantages of the following embodiments are not limited to theaforementioned advantages, and various other advantages may be evidentlyunderstood by those skilled in the art to which the embodiments pertainfrom the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included a part of thisspecification to provide a further understanding of this document,provide embodiments of the present invention and together with thedetailed description serve to explain the technical characteristics ofthe present invention.

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 5 shows the configuration of a known multi-input multi-output(MIMO) antenna communication system.

FIG. 6 is a diagram illustrating channels from a plurality oftransmission antennas to a single reception antenna.

FIG. 7 shows an example of component carriers and a componentaggregation in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 8 is a diagram for illustrating a contention-based random accessprocedure in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 9 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which an embodiment ofthe present invention may be applied.

FIG. 10 is a diagram illustrating a CSI-RS configuration in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 11 illustrates a system having a plurality oftransmission/reception antennas through which an eNB or a UE is capableof three-dimensional (3-D) beamforming based on an AAS in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 12 illustrates RSRP for each antenna port of an RRM-RS according toan embodiment of the present invention.

FIG. 13 illustrates RRM-RS antenna port grouping levels according to anembodiment of the present invention.

FIG. 14 is a diagram illustrating antenna ports and antenna port groupsof RRM-RSs arrayed in 2-D indices according to an embodiment of thepresent invention.

FIGS. 15 to 17 are diagrams illustrating examples of a CSI measurementand reporting method proposed by this specification.

FIG. 18 is a block diagram of a wireless communication apparatusaccording to an embodiment of the present invention.

MODE FOR INVENTION

Hereafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Adetailed description to be disclosed hereinbelow together with theaccompanying drawing is to describe embodiments of the present inventionand not to describe a unique embodiment for carrying out the presentinvention. The detailed description below includes details in order toprovide a complete understanding. However, those skilled in the art knowthat the present invention can be carried out without the details.

In some cases, in order to prevent a concept of the present inventionfrom being ambiguous, known structures and devices may be omitted or maybe illustrated in a block diagram format based on core function of eachstructure and device.

In the specification, a base station means a terminal node of a networkdirectly performing communication with a terminal. In the presentdocument, specific operations described to be performed by the basestation may be performed by an upper node of the base station in somecases. That is, it is apparent that in the network constituted bymultiple network nodes including the base station, various operationsperformed for communication with the terminal may be performed by thebase station or other network nodes other than the base station. A basestation (BS) may be generally substituted with terms such as a fixedstation, Node B, evolved-NodeB (eNB), a base transceiver system (BTS),an access point (AP), and the like. Further, a ‘terminal’ may be fixedor movable and be substituted with terms such as user equipment (UE), amobile station (MS), a user terminal (UT), a mobile subscriber station(MSS), a subscriber station (SS), an advanced mobile station (AMS), awireless terminal (WT), a Machine-Type Communication (MTC) device, aMachine-to-Machine (M2M) device, a Device-to-Device (D2D) device, andthe like.

Hereinafter, a downlink means communication from the base station to theterminal and an uplink means communication from the terminal to the basestation. In the downlink, a transmitter may be a part of the basestation and a receiver may be a part of the terminal. In the uplink, thetransmitter may be a part of the terminal and the receiver may be a partof the base station.

Specific terms used in the following description are provided to helpappreciating the present invention and the use of the specific terms maybe modified into other forms within the scope without departing from thetechnical spirit of the present invention.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), non-orthogonal multiple access (NOMA), and the like. The CDMAmay be implemented by radio technology universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented by radiotechnology such as Global System for Mobile communications (GSM)/GeneralPacket Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution(EDGE). The OFDMA may be implemented as radio technology such as IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (Evolved UTRA),and the like. The UTRA is a part of a universal mobile telecommunicationsystem (UMTS). 3rd generation partnership project (3GPP) long termevolution (LTE) as a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) adopts the OFDMA in a downlink and theSC-FDMA in an uplink. LTE-advanced (A) is an evolution of the 3GPP LTE.

The embodiments of the present invention may be based on standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2 whichare the wireless access systems. That is, steps or parts which are notdescribed to definitely show the technical spirit of the presentinvention among the embodiments of the present invention may be based onthe documents. Further, all terms disclosed in the document may bedescribed by the standard document.

3GPP LTE/LTE-A is primarily described for clear description, buttechnical features of the present invention are not limited thereto.

General Wireless Communication System to which an Embodiment of thePresent Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a type 1 radio frame structure capable of beingapplied to frequency division duplex (FDD) and a type 2 radio framestructure capable of being applied to time division duplex (TDD).

In FIG. 1, the size of the radio frame in a time domain is expressed ina multiple of a time unit “T_s=1/(15000*2048).” Downlink and uplinktransmission includes a radio frame having an interval ofT_f=307200*T_s=10 ms.

FIG. 1(a) illustrates the type 1 radio frame structure. The type 1 radioframe may be applied to both full duplex FDD and half duplex FDD.

The radio frame includes 10 subframes. One radio frame includes 20 slotseach having a length of T_slot=15360*T_s=0.5 ms. Indices 0 to 19 areassigned to the respective slots. One subframe includes two contiguousslots in the time domain, and a subframe i includes a slot 2i and a slot2i+1. The time taken to send one subframe is called a transmission timeinterval (TTI). For example, the length of one subframe may be 1 ms, andthe length of one slot may be 0.5 ms.

In FDD, uplink transmission and downlink transmission are classified inthe frequency domain. There is no restriction to full duplex FDD,whereas a UE is unable to perform transmission and reception at the sametime in a half duplex FDD operation.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in the time domain and includes a pluralityof resource blocks (RBs) in the frequency domain. An OFDM symbol is forexpressing one symbol period because 3GPP LTE uses OFDMA in downlink.The OFDM symbol may also be called an SC-FDMA symbol or a symbol period.The resource block is a resource allocation unit and includes aplurality of contiguous subcarriers in one slot.

FIG. 1(b) shows the type 2 radio frame structure.

The type 2 radio frame structure includes 2 half frames each having alength of 153600*T_s=5 ms. Each of the half frames includes 5 subframeseach having a length of 30720*T_s=1 ms.

In the type 2 radio frame structure of a TDD system, an uplink-downlinkconfiguration is a rule showing how uplink and downlink are allocated(or reserved) with respect to all of subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 DOWN- LINK- TO- UPLINK- UPLINK DOWN- SWITCH- LINK POINT CONFIG-PERIO- SUBFRAME NUMBER URATION DICITY 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U UU D S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10ms  D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D DD D D D D 6 5 ms D S U U U D S U U D

Referring to Table 1, “D” indicates a subframe for downlinktransmission, “U” indicates a subframe for uplink transmission, and “S”indicates a special subframe including the three fields of a downlinkpilot time slot (DwPTS), a guard period (GP), and an uplink pilot timeslot (UpPTS) for each of the subframes of the radio frame.

The DwPTS is used for initial cell search, synchronization or channelestimation by a UE. The UpPTS is used for an eNB to perform channelestimation and for a UE to perform uplink transmission synchronization.The GP is an interval for removing interference occurring in uplink dueto the multi-path delay of a downlink signal between uplink anddownlink.

Each subframe i includes the slot 2i and the slot 2i+1 each having“T_slot=15360*T_s=0.5 ms.”

The uplink-downlink configuration may be divided into seven types. Thelocation and/or number of downlink subframes, special subframes, anduplink subframes are different in the seven types.

A point of time changed from downlink to uplink or a point of timechanged from uplink to downlink is called a switching point.Switch-point periodicity means a cycle in which a form in which anuplink subframe and a downlink subframe switch is repeated in the samemanner. The switch-point periodicity supports both 5 ms and 10 ms. Inthe case of a cycle of the 5 ms downlink-uplink switching point, thespecial subframe S is present in each half frame. In the case of thecycle of the 5 ms downlink-uplink switching point, the special subframeS is present only in the first half frame.

In all of the seven configurations, No. 0 and No. 5 subframes and DwPTSsare an interval for only downlink transmission. The UpPTSs, thesubframes, and a subframe subsequent to the subframes are always aninterval for uplink transmission.

Both an eNB and a UE may be aware of such uplink-downlink configurationsas system information. The eNB may notify the UE of a change in theuplink-downlink allocation state of a radio frame by sending only theindex of configuration information whenever uplink-downlinkconfiguration information is changed. Furthermore, the configurationinformation is a kind of downlink control information. Like schedulinginformation, the configuration information may be transmitted through aphysical downlink control channel (PDCCH) and may be transmitted to allof UEs within a cell in common through a broadcast channel as broadcastinformation.

Table 2 shows a configuration (i.e., the length of a DwPTS/GP/UpPTS) ofthe special subframe.

TABLE 2 Normal cyclic prefix in downlink UpPTS Extended cyclic prefix indownlink Normal UpPTS cyclic Extended Normal Special prefix cycliccyclic Extended subframe in prefix prefix in cyclic prefix configurationDwPTS uplink in uplink DwPTS uplink in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120· T_(s) 5  6592 ·T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of the radio frame according to the example of FIG. 1 isonly one example. The number of subcarriers included in one radio frame,the number of slots included in one subframe, and the number of OFDMsymbols included in one slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin the wireless communication system to which the present invention canbe applied.

Referring to FIG. 2, one downlink slot includes the plurality of OFDMsymbols in the time domain. Herein, it is exemplarily described that onedownlink slot includes 7 OFDM symbols and one resource block includes 12subcarriers in the frequency domain, but the present invention is notlimited thereto.

Each element on the resource grid is referred to as a resource elementand one resource block includes 12×7 resource elements. The number ofresource blocks included in the downlink slot, NDL is subordinated to adownlink transmission bandwidth.

A structure of the uplink slot may be the same as that of the downlinkslot.

FIG. 3 illustrates a structure of a downlink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 3, a maximum of three former OFDM symbols in the firstslot of the sub frame is a control region to which control channels areallocated and residual OFDM symbols is a data region to which a physicaldownlink shared channel (PDSCH) is allocated. Examples of the downlinkcontrol channel used in the 3GPP LTE include a Physical Control FormatIndicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH),a Physical Hybrid-ARQ Indicator Channel (PHICH), and the like.

The PFCICH is transmitted in the first OFDM symbol of the subframe andtransports information on the number (that is, the size of the controlregion) of OFDM symbols used for transmitting the control channels inthe subframe. The PHICH which is a response channel to the uplinktransports an Acknowledgement (ACK)/Not-Acknowledgement (NACK) signalfor a hybrid automatic repeat request (HARQ). Control informationtransmitted through a PDCCH is referred to as downlink controlinformation (DCI). The downlink control information includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for apredetermined terminal group.

The PDCCH may transport A resource allocation and transmission format(also referred to as a downlink grant) of a downlink shared channel(DL-SCH), resource allocation information (also referred to as an uplinkgrant) of an uplink shared channel (UL-SCH), paging information in apaging channel (PCH), system information in the DL-SCH, resourceallocation for an upper-layer control message such as a random accessresponse transmitted in the PDSCH, an aggregate of transmission powercontrol commands for individual terminals in the predetermined terminalgroup, a voice over IP (VoIP). A plurality of PDCCHs may be transmittedin the control region and the terminal may monitor the plurality ofPDCCHs. The PDCCH is constituted by one or an aggregate of a pluralityof continuous control channel elements (CCEs). The CCE is a logicalallocation wise used to provide a coding rate depending on a state of aradio channel to the PDCCH. The CCEs correspond to a plurality ofresource element groups. A format of the PDCCH and a bit number ofusable PDCCH are determined according to an association between thenumber of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to betransmitted and attaches the control information to a cyclic redundancycheck (CRC) to the control information. The CRC is masked with a uniqueidentifier (referred to as a radio network temporary identifier (RNTI))according to an owner or a purpose of the PDCCH. In the case of a PDCCHfor a specific terminal, the unique identifier of the terminal, forexample, a cell-RNTI (C-RNTI) may be masked with the CRC. Alternatively,in the case of a PDCCH for the paging message, a paging indicationidentifier, for example, the CRC may be masked with a paging-RNTI(P-RNTI). In the case of a PDCCH for the system information, in moredetail, a system information block (SIB), the CRC may be masked with asystem information identifier, that is, a system information (SI)-RNTI.The CRC may be masked with a random access (RA)-RNTI in order toindicate the random access response which is a response to transmissionof a random access preamble.

FIG. 4 illustrates a structure of an uplink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 4, the uplink subframe may be divided into the controlregion and the data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) transporting uplink control information isallocated to the control region. A physical uplink shared channel(PUSCH) transporting user data is allocated to the data region. Oneterminal does not simultaneously transmit the PUCCH and the PUSCH inorder to maintain a single carrier characteristic.

A resource block (RB) pair in the subframe are allocated to the PUCCHfor one terminal. RBs included in the RB pair occupy differentsubcarriers in two slots, respectively. The RB pair allocated to thePUCCH frequency-hops in a slot boundary.

Multi-Input Multi-Output (MIMO)

An MIMO technology uses multiple transmitting (Tx) antennas and multiplereceiving (Rx) antennas by breaking from generally one transmittingantenna and one receiving antenna up to now. In other words, the MIMOtechnology is a technology for achieving capacity increment orcapability enhancement by using a multiple input multiple output antennaat a transmitter side or a receiver side of the wireless communicationsystem. Hereinafter, “MIMO” will be referred to as “multiple inputmultiple output antenna”.

More specifically, the MIMO technology does not depend on one antennapath in order to receive one total message and completes total data bycollecting a plurality of data pieces received through multipleantennas. Consequently, the MIMO technology may increase a data transferrate within in a specific system range and further, increase the systemrange through a specific data transfer rate.

In next-generation mobile communication, since a still higher datatransfer rate than the existing mobile communication is required, it isanticipated that an efficient multiple input multiple output technologyis particularly required. In such a situation, an MIMO communicationtechnology is a next-generation mobile communication technology whichmay be widely used in a mobile communication terminal and a relay andattracts a concern as a technology to overcome a limit of a transmissionamount of another mobile communication according to a limit situationdue to data communication extension, and the like.

Meanwhile, the multiple input multiple output (MIMO) technology amongvarious transmission efficiency improvement technologies which have beenresearched in recent years as a method that may epochally improve acommunication capacity and transmission and reception performancewithout additional frequency allocation or power increment has thelargest attention in recent years.

FIG. 5 is a configuration diagram of a general multiple input multipleoutput (MIMO) communication system.

Referring to FIG. 5, when the number of transmitting antennas increasesto NT and the number of receiving antennas increases to NR at the sametime, since a theoretical channel transmission capacity increases inproportion to the number of antennas unlike a case using multipleantennas only in a transmitter or a receiver, a transfer rate may beimproved and frequency efficiency may be epochally improved. In thiscase, the transfer rate depending on an increase in channel transmissioncapacity may theoretically increase to a value acquired by multiplying amaximum transfer rate (Ro) in the case using one antenna by a rateincrease rate (Ri) given below.

R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, for example, in an MIMO communication system using fourtransmitting antennas and four receiving antennas, a transfer rate whichis four times higher than a single antenna system may be acquired.

Such an MIMO antenna technology may be divided into a spatial diversityscheme increasing transmission reliability by using symbols passingthrough various channel paths and a spatial multiplexing schemeimproving the transfer rate by simultaneously transmitting multiple datasymbols by using multiple transmitting antennas. Further, a researchinto a scheme that intends to appropriately acquire respectiveadvantages by appropriately combining two schemes is also a field whichhas been researched in recent years.

The respective schemes will be described below in more detail.

First, the spatial diversity scheme includes a space-time block codingseries and a space-time Trelis coding series scheme simultaneously usinga diversity gain and a coding gain. In general, the Trelis is excellentin bit error rate enhancement performance and code generation degree offreedom, but the space-time block code is simple in operationalcomplexity. In the case of such a spatial diversity gain, an amountcorresponding to a multiple (NT×NR) of the number (NT) of transmittingantennas and the number (NR) of receiving antennas may be acquired.

Second, the spatial multiplexing technique is a method that transmitsdifferent data arrays in the respective transmitting antennas and inthis case, mutual interference occurs among data simultaneouslytransmitted from the transmitter in the receiver. The receiver receivesthe data after removing the interference by using an appropriate signalprocessing technique. A noise removing scheme used herein includes amaximum likelihood detection (MLD) receiver, a zero-forcing (ZF)receiver, a minimum mean square error (MMSE) receiver, a diagonal-belllaboratories layered space-time (D-BLAST), a vertical-bell laboratorieslayered space-time), and the like and in particular, when channelinformation may be known in the transmitter side, a singular valuedecomposition (SVD) scheme, and the like may be used.

Third, a technique combining the space diversity and the spatialmultiplexing may be provided. When only the spatial diversity gain isacquired, the performance enhancement gain depending on an increase indiversity degree is gradually saturated and when only the spatialmultiplexing gain is acquired, the transmission reliability deterioratesin the radio channel Schemes that acquire both two gains while solvingthe problem have been researched and the schemes include a space-timeblock code (Double-STTD), a space-time BICM (STBICM), and the like.

In order to describe a communication method in the MIMO antenna systemdescribed above by a more detailed method, when the communication methodis mathematically modeled, the mathematical modeling may be shown asbelow.

First, it is assumed that NT transmitting antennas and NR receivingantennas are present as illustrated in FIG. 5.

First, in respect to a transmission signal, when NT transmittingantennas are provided, NT may be expressed as a vector given belowbecause the maximum number of transmittable information is NT.

s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

Transmission power may be different in the respective transmissioninformation s1, s2, sNT and in this case, when the respectivetransmission power is P1, P2, . . . , PNT, the transmission informationof which the transmission power is adjusted may be expressed as a vectorgiven below.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

Further, ŝ may be expressed as described below as a diagonal matrix P ofthe transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T\;}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

The information vector ŝ of which the transmission power is adjusted ismultiplied by a weight matrix W to constitute NT transmission signalsx1, x2, . . . , xNT which are actually transmitted. Herein, the weightmatrix serves to appropriately distribute the transmission informationto the respective antennas according to a transmission channelsituation, and the like. The transmission signals x1, x2, . . . , xNTmay be expressed as below by using a vector x.

$\begin{matrix}\begin{matrix}{x = \begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix}} \\{= {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}} \\{= {{W\hat{s}} = {WPs}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

In Equation 5, wij represents a weight between the i-th transmittingantenna and j-th transmission information and W represents the weight asthe matrix. The matrix W is called a weight matrix or a precodingmatrix.

The transmission signal x described above may be divided intotransmission signals in a case using the spatial diversity and a caseusing the spatial multiplexing.

In the case using the spatial multiplexing, since different signals aremultiplexed and sent, all elements of an information vector s havedifferent values, while when the spatial diversity is used, since thesame signal is sent through multiple channel paths, all of the elementsof the information vector s have the same value.

A method mixing the spatial multiplexing and the spatial diversity mayalso be considered. That is, for example, a case may also be consideredin which the same signal is transmitted using the spatial diversitythrough three transmitting antennas and different signals are sent byspatial multiplexing through residual transmitting antennas.

Next, when NR receiving antennas are provided, received signals y1, y2,. . . , yNR of the respective antennas are expressed as a vector y asdescribed below.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO antenna communication system, thechannels may be distinguished based on transmitting and receivingantenna indexes and a channel passing through a receiving antenna i froma transmitting antenna j will be represented as hij. Herein, it is notedthat in the case of the order of the index of hij, the receiving antennaindex is earlier and the transmitting antenna index is later.

The multiple channels are gathered into one to be expressed even asvector and matrix forms. An example of expression of the vector will bedescribed below.

FIG. 6 is a diagram illustrating a channel from multiple transmittingantennas to one receiving antenna.

As illustrated in FIG. 6, a channel which reaches receiving antenna Ifrom a total of NT transmitting antennas may be expressed as below.

h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Further, all of channels passing through NR receiving antennas from NTtransmitting antennas may be shown as below through matrix expressionshown in Equation given above.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Since additive white Gaussian noise (AWGN) is added after passingthrough a channel matrix H given above in an actual channel, whitenoises n1, n2, . . . , nNR added to NR receiving antennas, respectivelyare expressed as below.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Each of the transmission signal, the reception signal, the channel, andthe white noise in the MIMO antenna communication system may beexpressed through a relationship given below by modeling thetransmission signal, the reception signal, the channel, and the whitenoise.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}} & \left\lbrack {{Equation}\mspace{14mu} 9} \right\rbrack\end{matrix}$

The number of rows and columns of the channel matrix H representing thestate of the channel is determined by the number of transmitting andreceiving antennas. In the case of the channel matrix H, the number ofrows becomes equivalent to NR which is the number of receiving antennasand the number of columns becomes equivalent to NR which is the numberof transmitting antennas. That is, the channel matrix H becomes an NR xNR matrix.

In general, a rank of the matrix is defined as the minimum number amongthe numbers of independent rows or columns. Therefore, the rank of thematrix may not be larger than the number of rows or columns. As anequation type example, the rank (rank(H)) of the channel matrix H islimited as below.

rank(H)≦min(N _(T) ,T _(R))  [Equation 11]

Further, when the matrix is subjected to Eigen value decomposition, therank may be defined as not 0 but the number of Eigen values among theEigen values. By a similar method, when the rank is subjected tosingular value decomposition, the rank may be defined as not 0 but thenumber of singular values. Accordingly, a physical meaning of the rankin the channel matrix may be the maximum number which may send differentinformation in a given channel.

In this specification, a ‘rank’ for MIMO transmission represents thenumber of paths to independently transmit the signal at a specific timeand in a specific frequency resource and ‘the number of layers’represents the number of signal streams transmitted through each path.In general, since the transmitter side transmits layers of the numbercorresponding to the number of ranks used for transmitting the signal,the rank has the same meaning as the number layers if not particularlymentioned.

Carrier Aggregation

A communication environment considered in embodiments of the presentinvention includes multi-carrier supporting environments. That is, amulti-carrier system or a carrier aggregation system used in the presentinvention means a system that aggregates and uses one or more componentcarriers (CCs) having a smaller bandwidth smaller than a target band atthe time of configuring a target wideband in order to support awideband.

In the present invention, a multi-carrier means an aggregation ofcarriers (alternatively carrier aggregation). In this case, theaggregation of carriers means both an aggregation between continuouscarriers and an aggregation between non-contiguous carriers. Further,the number of component carriers aggregated between downlink and uplinkmay be differently set. A case where the number of downlink componentcarriers (hereinafter referred to as a “DL CC”) and the number of uplinkcomponent carriers (hereinafter, referred to as an “UL CC”) are the sameis referred to as a “symmetric aggregation”, and a case where the numberof downlink component carriers and the number of uplink componentcarriers are different is referred to as an “asymmetric aggregation.”The carrier aggregation may be used interchangeably with a term, such asa bandwidth aggregation or a spectrum aggregation.

A carrier aggregation configured by combining two or more componentcarriers aims at supporting up to a bandwidth of 100 MHz in the LTE-Asystem. When one or more carriers having the bandwidth than the targetband are combined, the bandwidth of the carriers to be combined may belimited to a bandwidth used in the existing system in order to maintainbackward compatibility with the existing IMT system. For example, theexisting 3GPP LTE system supports bandwidths of 1.4, 3, 5, 10, 15, and20 MHz and a 3GPP LTE-advanced system (that is, LTE-A) may be configuredto support a bandwidth larger than 20 MHz by using on the bandwidth forcompatibility with the existing system. Further, the carrier aggregationsystem used in the preset invention may be configured to support thecarrier aggregation by defining a new bandwidth regardless of thebandwidth used in the existing system.

The LTE-A system uses a concept of the cell in order to manage a radioresource.

The carrier aggregation environment may be called a multi-cellenvironment. The cell is defined as a combination of a pair of adownlink resource (DL CC) and an uplink resource (UL CC), but the uplinkresource is not required. Therefore, the cell may be constituted by onlythe downlink resource or both the downlink resource and the uplinkresource. When a specific terminal has only one configured serving cell,the cell may have one DL CC and one UL CC, but when the specificterminal has two or more configured serving cells, the cell has DL CCsas many as the cells and the number of UL CCs may be equal to or smallerthan the number of DL CCs.

Alternatively, contrary to this, the DL CC and the UL CC may beconfigured. That is, when the specific terminal has multiple configuredserving cells, a carrier aggregation environment having UL CCs more thanDL CCs may also be supported. That is, the carrier aggregation may beappreciated as aggregation of two or more cells having different carrierfrequencies (center frequencies). Herein, the described ‘cell’ needs tobe distinguished from a cell as an area covered by the base stationwhich is generally used.

The cell used in the LTE-A system includes a primary cell (PCell) and asecondary cell (SCell. The P cell and the S cell may be used as theserving cell. In a terminal which is in an RRC_CONNECTED state, but doesnot have the configured carrier aggregation or does not support thecarrier aggregation, only one serving constituted by only the P cell ispresent. On the contrary, in a terminal which is in the RRC_CONNECTEDstate and has the configured carrier aggregation, one or more servingcells may be present and the P cell and one or more S cells are includedin all serving cells.

The serving cell (P cell or S cell) may be configured through an RRCparameter. PhysCellId as a physical layer identifier of the cell hasinteger values of 0 to 503. SCellIndex as a short identifier used toidentify the S cell has integer values of 1 to 7. ServCellIndex as ashort identifier used to identify the serving cell (P cell or S cell)has the integer values of 0 to 7. The value of 0 is applied to the Pcell and SCellIndex is previously granted for application to the S cell.That is, a cell having a smallest cell ID (alternatively, cell index) inServCellIndex becomes the P cell.

The P cell means a cell that operates on a primary frequency(alternatively a primary CC). The terminal may be used to perform aninitial connection establishment process or a connectionre-establishment process and may be designated as a cell indicatedduring a handover process. Further, the P cell means a cell whichbecomes the center of control associated communication among servingcells configured in the carrier aggregation environment. That is, theterminal may be allocated with and transmit the PUCCH only in the P cellthereof and use only the P cell to acquire the system information orchange a monitoring procedure. An evolved universal terrestrial radioaccess (E-UTRAN) may change only the P cell for the handover procedureto the terminal supporting the carrier aggregation environment by usingan RRC connection reconfiguration message (RRCConnectionReconfiguration)message of an upper layer including mobile control information(mobilityControlInfo).

The S cell means a cell that operates on a secondary frequency(alternatively, secondary CC). Only one P cell may be allocated to aspecific terminal and one or more S cells may be allocated to thespecific terminal. The S cell may be configured after RRC connectionestablishment is achieved and used for providing an additional radioresource. The PUCCH is not present in residual cells other than the Pcell, that is, the S cells among the serving cells configured in thecarrier aggregation environment. The E-UTRAN may provide all systeminformation associated with a related cell which is in an RRC_CONNECTEDstate through a dedicated signal at the time of adding the S cells tothe terminal that supports the carrier aggregation environment. A changeof the system information may be controlled by releasing and adding therelated S cell and in this case, the RRC connection reconfiguration(RRCConnectionReconfiguration) message of the upper layer may be used.The E-UTRAN may perform having different parameters for each terminalrather than broadcasting in the related S cell.

After an initial security activation process starts, the E-UTRAN addsthe S cells to the P cell initially configured during the connectionestablishment process to configure a network including one or more Scells. In the carrier aggregation environment, the P cell and the S cellmay operate as the respective component carriers. In an embodimentdescribed below, the primary component carrier (PCC) may be used as thesame meaning as the P cell and the secondary component carrier (SCC) maybe used as the same meaning as the S cell.

FIG. 7 illustrates examples of a component carrier and carrieraggregation in the wireless communication system to which the presentinvention can be applied.

FIG. 7a illustrates a single carrier structure used in an LTE system.The component carrier includes the DL CC and the UL CC. One componentcarrier may have a frequency range of 20 MHz.

FIG. 7b illustrates a carrier aggregation structure used in the LTEsystem. In the case of FIG. 7b , a case is illustrated, in which threecomponent carriers having a frequency magnitude of 20 MHz are combined.Each of three DL CCs and three UL CCs is provided, but the number of DLCCs and the number of UL CCs are not limited. In the case of carrieraggregation, the terminal may simultaneously monitor three CCs, andreceive downlink signal/data and transmit uplink signal/data.

When N DL CCs are managed in a specific cell, the network may allocate M(M≦N) DL CCs to the terminal. In this case, the terminal may monitoronly M limited DL CCs and receive the DL signal. Further, the networkgives L (L≦M≦N) DL CCs to allocate a primary DL CC to the terminal andin this case, UE needs to particularly monitor L DL CCs. Such a schememay be similarly applied even to uplink transmission.

A linkage between a carrier frequency (alternatively, DL CC) of thedownlink resource and a carrier frequency (alternatively, UL CC) of theuplink resource may be indicated by an upper-layer message such as theRRC message or the system information. For example, a combination of theDL resource and the UL resource may be configured by a linkage definedby system information block type 2 (SIB2). In detail, the linkage maymean a mapping relationship between the DL CC in which the PDCCHtransporting a UL grant and a UL CC using the UL grant and mean amapping relationship between the DL CC (alternatively, UL CC) in whichdata for the HARQ is transmitted and the UL CC (alternatively, DL CC) inwhich the HARQ ACK/NACK signal is transmitted.

If one or more S cells are configured in a UE, a network may activate ordeactivate the configured S cell(s). A P cell is always activated. Thenetwork activates or deactivates the S cell(s) by sending anactivation/deactivation MAC control element.

The activation/deactivation MAC control element has a fixed size andincludes a single octet including seven C fields and one R field. The Cfield is configured for each S cell index “SCellIndex”, and indicatesthe activation/deactivation state of the S cell. When the value of the Cfield is set to “1”, it indicates that an S cell having a correspondingS cell index is activated. When the value of the C field is set to “0”,it indicates that an S cell having a corresponding S cell index isdeactivated.

Furthermore, the UE maintains a timer “sCellDeactivationTimer” for eachconfigured S cell and deactivates a related S cell when the timerexpires. The same initial value of the timer is applied to each instanceof the timer “sCellDeactivationTimer” and set by RRC signaling. When theS cell(s) are added or after handover, initial S cell(s) are adeactivation state.

The UE performs the following operation on each of the configured Scell(s) in each TTI.

-   -   When the UE receives an activation/deactivation MAC control        element that activates an S cell in a specific TTI (subframe n),        the UE activates the S cell in a corresponding TTI (a subframe        n+8 or thereafter) on predetermined timing and (re)starts a        timer related to the corresponding S cell. What the UE activates        the S cell means that the UE applies a common S cell operation,        such as the transmission of a sounding reference signal (SRS),        the reporting of a channel quality indicator (CQI)/precoding        matrix indicator (PMI)/rank indication (RI)/precoding type        indicator (PTI), the monitoring of a PDCCH and the monitoring of        a PDCCH for an S cell on the S cell.    -   When the UE receives an activation/deactivation MAC control        element that deactivates an S cell in a specific TTI        (subframe n) or a timer related to a specific TTI (subframe        n)-activated S cell expires, the UE deactivates the S cell in a        corresponding TTI (subframe n+8 or thereafter) on predetermined        timing, stops the timer of the corresponding S cell, and flushes        all of HARQ buffers related to the corresponding S cell.    -   If a PDCCH on an activated S cell indicates an uplink grant or        downlink assignment or a PDCCH on a serving cell that schedules        the activated S cell indicates an uplink grant or downlink        assignment for the activated S cell, the UE restarts a timer        related to the corresponding S cell.    -   When the S cell is deactivated, the UE does not send an SRS on        the S cell, does not report a CQI/PMI/RI/PTI for the S cell,        does not send an UL-SCH on the S cell, and does not monitor a        PDCCH on the S cell.

Random Access Procedure

A random access procedure provided by LTE/LTE-A systems is describedbelow.

The random access procedure is used for a UE to obtain uplinksynchronization with an eNB or to have uplink radio resources allocatedthereto. When the UE is powered on, the UE obtains downlinksynchronization with an initial cell and receives system information.The UE obtains information about a set of available random accesspreambles and radio resources used to send a random access preamble fromthe system information. The radio resources used to send the randomaccess preamble may be specified as a combination of at least onesubframe index and an index in a frequency domain. The UE sends a randomaccess preamble randomly selected from the set of random accesspreambles. An eNB that has received the random access preamble sends atiming alignment (TA) value for uplink synchronization to the UE througha random access response. Accordingly, the UE obtains uplinksynchronization.

The random access procedure is common to frequency division duplex (FDD)and time division duplex (TDD). The random access procedure is notrelated to a cell size and is also not related to the number of servingcells if a component aggregation (CA) has been configured.

First, the UE may perform the random access procedure as in thefollowing cases.

-   -   If the UE performs initial access in the RRC idle state because        it does not have RRC connection with the eNB    -   If the UE performs an RRC connection re-establishment procedure    -   If the UE first accesses a target cell in a handover process    -   If the random access procedure is requested by a command from        the eNB    -   If there is data to be transmitted in downlink in an uplink        non-synchronized situation during the RRC connection state    -   If there is a data to be transmitted in uplink in an uplink        non-synchronized situation or in a situation in which designated        radio resources used to request radio resources have not been        allocated during the RRC connection state    -   If the positioning of the UE is performed in a situation in        which timing advance is necessary during the RRC connection        state    -   If a recovery process is performed when a radio link failure or        handover failure occurs

In 3GPP Rel-10, a method for applying a timing advance (TA) valueapplicable to one specific cell (e.g., a P cell) to a plurality of cellsin common in a radio access system supporting a component aggregationhas been taken into consideration. A UE may aggregate a plurality ofcells belonging to different frequency bands (i.e., greatly spaced aparton the frequency) or a plurality of cells having different propagationproperties. Furthermore, in the case of a specific cell, in order toexpand coverage or remove a coverage hole, if the UE performscommunication with an eNB (i.e., a macro eNB) through one cell andperforms communication with a secondary eNB (SeNB) through the othercell in a situation in which a remote radio header (RRH) (i.e.,repeater), a small cell such as a femto cell or a pico cell, or the SeNBhas been disposed within the cell, a plurality of cells may havedifferent delay properties. In this case, if the UE performs uplinktransmission using a method for applying one TA value to a plurality ofcells in common, the synchronization of an uplink signal transmitted onthe plurality of cells may be severely influenced. Accordingly, aplurality of TAs may be used in a CA situation in which a plurality ofcells has been aggregated. In 3GPP Rel-11, in order to support multipleTAs, the independent allocation of the TAs may be taken intoconsideration for each specific cell group. This is called a TA group(TAG). The TAG may include one or more cells. The same TA may be appliedto one or more cells included in a TAG in common. In order to supportsuch multiple TAs, an MAC TA command control element includes a TAGidentity (ID) of 2 bits and a TA command field of 6 bits.

A UE in which a CA has been configured performs a random accessprocedure if it performs the random access procedure in relation to a Pcell. In the case of a TAG to which the P cell belongs (i.e., a primaryTAG (pTAG)), as in a conventional technology, TA determined based on theP cell or coordinated through a random access procedure involved in theP cell may be applied to all of cell(s) within the pTAG. In contrast, inthe case of a TAG including only an S cell (i.e., a secondary TAG(sTAG)), TA determined based on a specific S cell within the sTAG may beapplied to all of cell(s) within the corresponding sTAG. In this case,the TA may be obtained by a random access procedure initiated by an eNB.More specifically, the S cell is configured as a random access channel(RACH) resource within the sTAG. In order to determine the TA, the eNBrequests RACH access in the S cell. That is, the eNB initiates RACHtransmission on S cells in response to a PDCCH order transmitted in theP cell. A response message for an S cell preamble is transmitted througha P cell using an RA-RNTI. The UE may apply TA, determined based on an Scell to which random access has been successfully completed, to all ofcell(s) within a corresponding sTAG. As described above, the randomaccess procedure may be performed even in an S cell in order to obtainthe TA of an sTAG to which the S cell belongs even in the correspondingS cell.

An LTE/LTE-A system provides a contention-based random access procedurefor randomly selecting, by a UE, one preamble within a specific set andusing the selected preamble and a non-contention-based random accessprocedure for using a random access preamble allocated to only aspecific UE by an eNB in a process of selecting a random access preamble(RACH preamble). In this case, the non-contention-based random accessprocedure may be used for only UE positioning and/or timing advancealignment for an sTAG if it is requested in the handover process or inresponse to a command from the eNB. After the random access procedure iscompleted, common uplink/downlink transmission is performed.

A relay node (RN) also supports both the contention-based random accessprocedure and the non-contention-based random access procedure. When arelay node performs the random access procedure, it suspends an RNsubframe configuration at that point of time. That is, this means thatit temporarily discards an RN subframe. Thereafter, an RN subframeconfiguration is restarted at a point of time at which a random accessprocedure is successfully completed.

FIG. 8 is a diagram for illustrating a contention-based random accessprocedure in a wireless communication system to which an embodiment ofthe present invention may be applied.

(1) First Message (Msg 1 or Message 1)

First, UE randomly selects one random access preamble (RACH preamble)from a set of random access preambles indicated by system information ora handover command, selects a physical RACH (PRACH) resource capable ofsending the random access preamble, and sends the selected physical RACH(PRACH).

The random access preamble is transmitted through 6 bits in an RACHtransport channel. The 6 bits include a random identity of 5 bits foridentifying the UE that has performed RACH transmission and 1 bit (e.g.,indicate the size of a third message Msg3) for indicating additionalinformation.

An eNB that has received the random access preamble from the UE decodesthe random access preamble and obtains an RA-RNTI. The RA-RNTI relatedto the PRACH in which the random access preamble has been transmitted isdetermined by the time-frequency resource of the random access preambletransmitted by the corresponding UE.

(2) Second Message (Msg 2 or Message 2)

The eNB sends a random access response, addressed by the RA-RNTIobtained through the preamble on the first message, to the UE. Therandom access response may include a random access (RA) preambleindex/identifier, uplink (UL) assignment providing notification ofuplink radio resources, a temporary C-RNTI, and a time alignment command(TAC). The TAC is information indicative of a time alignment commandthat is transmitted from the eNB to the UE in order to maintain uplinktime alignment. The UE updates uplink transmission timing using the TAC.When the UE updates time synchronization, it initiates or restarts atime alignment timer. An UL grant includes uplink resource allocationused for the transmission of a scheduling message (third message) to bedescribed later and a transmit power command (TPC). The TPC is used todetermine transmission power for a scheduled PUSCH.

After the UE sends the random access preamble, it attempts to receiveits own random access response within a random access response windowindicated by the eNB through system information or a handover command,detects a PDCCH masked with an RA-RNTI corresponding to the PRACH, andreceives a PDSCH indicated by the detected PDCCH. Information about therandom access response may be transmitted in the form of a MAC packetdata unit (PDU). The MAC PDU may be transferred through the PDSCH. ThePDCCH may include information about the UE that needs to receive thePDSCH, information about the frequency and time of the radio resourcesof the PDSCH, and the transmission format of the PDSCH. As describedabove, once the UE successfully detects the PDCCH transmitted thereto,it may properly receive the random access response transmitted throughthe PDSCH based on the pieces of information of the PDCCH.

The random access response window means a maximum time interval duringwhich the UE that has sent the preamble waits to receive the randomaccess response message. The random access response window has a lengthof “ra-ResponseWindowSize” that starts from a subframe subsequent tothree subframes from the last subframe in which the preamble istransmitted. That is, the UE waits to receive the random access responseduring a random access window secured after three subframes from asubframe in which the preamble has been transmitted. The UE may obtainthe parameter value of a random access window size“ra-ResponseWindowsize” through the system information. The randomaccess window size may be determined to be a value between 2 and 10.

When the UE successfully receives the random access response having thesame random access preamble index/identifier as the random accesspreamble transmitted to the eNB, it suspends the monitoring of therandom access response. In contrast, if the UE has not received a randomaccess response message until the random access response window isterminated or the UE does not receive a valid random access responsehaving the same random access preamble index as the random accesspreamble transmitted to the eNB, the UE considers the reception of arandom access response to be a failure and then may perform preambleretransmission.

As described above, the reason why the random access preamble index isnecessary for the random access response is to provide notification thatan UL grant, a TC-RNTI and a TAC are valid for which UE because randomaccess response information for one or more UEs may be included in onerandom access response.

(3) Third Message (Msg 3 or Message 3)

When the UE receives a valid random access response, it processes eachof pieces of information included in the random access response. Thatis, the UE applies a TAC to each of the pieces of information and storesa TC-RNTI. Furthermore, the UE sends data, stored in the buffer of theUE, or newly generated data to the eNB using an UL grant. If the UEperforms first connection, an RRC connection request generated in theRRC layer and transferred through a CCCH may be included in the thirdmessage and transmitted. In the case of an RRC connectionre-establishment procedure, an RRC connection re-establishment requestgenerated in the RRC layer and transferred through a CCCH may beincluded in the third message and transmitted. Furthermore, the thirdmessage may include an NAS access request message.

The third message may include the identity of the UE. In thecontention-based random access procedure, the eNB is unable to determinewhich UE can perform the random access procedure. The reason for this isthat the UE has to be identified in order to perform a collisionresolution.

A method for including the identity of UE includes two methods. In thefirst method, if UE has already had a valid cell identity (C-RNTI)allocated in a corresponding cell prior to a random access procedure,the UE sends its own cell identity through an uplink transmission signalcorresponding to an UL grant. In contrast, if a valid cell identity hasnot been allocated to the UE prior to a random access procedure, the UEincludes its own unique identity (e.g., an S-TMSI or a random number) inan uplink transmission signal and sends the uplink transmission signal.In general, the unique identity is longer than a C-RNTI. In transmissionon an UL-SCH, UE-specific scrambling is used. In this case, if a C-RNTIhas not been allocated to the UE, the scrambling may not be based on theC-RNTI, and instead a TC-RNTI received in a random access response isused. If the UE has sent data corresponding to the UL grant, itinitiates a timer for a collision resolution (i.e., a contentionresolution timer).

(4) Fourth Message (Msg 4 or Message 4)

When the C-RNTI of the UE is received through the third message from theUE, the eNB sends a fourth message to the UE using the received C-RNTI.In contrast, when the eNB receives a unique identity (i.e., an S-TMSI ora random number) through the third message from the UE, it sends thefourth message to the UE using a TC-RNTI allocated to the correspondingUE in a random access response. In this case, the fourth message maycorrespond to an RRC connection setup message including a C-RNTI.

After the UE sends data including its own identity through the UL grantincluded in the random access response, it waits for an instruction fromthe eNB for a collision resolution. That is, the UE attempts to receivea PDCCH in order to receive a specific message. A method for receivingthe PDCCH includes two methods. As described above, if the third messagetransmitted in response to the UL grant includes a C-RNTI as its ownidentity, the UE attempts the reception of a PDCCH using its own C-RNTI.If the identity is a unique identity (i.e., an S-TMSI or a randomnumber), the UE attempts the reception of a PDCCH using a TC-RNTIincluded in the random access response. Thereafter, in the former case,if the UE has received a PDCCH through its own C-RNTI before a collisionresolution timer expires, the UE determines that the random accessprocedure has been normally performed and terminates the random accessprocedure. In the latter case, if the UE has received a PDCCH through aTC-RNTI before a collision resolution timer expires, the UE checks datain which a PDSCH indicated by the PDCCH is transferred. If, as a resultof the check, it is found that the unique identity of the UE has beenincluded in the contents of the data, the UE determines that the randomaccess procedure has been normally performed and terminates the randomaccess procedure. The UE obtains the C-RNTI through the fourth message.Thereafter, the UE and a network send or receive a UE-dedicated messageusing the C-RNTI.

A method for a collision resolution in random access is described below.

The reason why a collision occurs in performing random access is thatthe number of random access preambles is basically limited. That is, aUE randomly selects one of common random access preambles and sends theselected random access preamble because an eNB cannot assign a randomaccess preamble unique to a UE to all of UEs. Accordingly, two or moreUEs may select the same random access preamble and send it through thesame radio resources (PRACH resource), but the eNB determines thereceived random access preambles to be one random access preambletransmitted by one UE. For this reason, the eNB sends a random accessresponse to the UE, and expects that the random access response will bereceived by one UE. As described above, however, since a collision mayoccur, two or more UEs receive one random access response and thus theeNB performs an operation according to the reception of each randomaccess response for each UE. That is, there is a problem in that the twoor more UEs send different data through the same radio resources usingone UL grant included in the random access response. Accordingly, thetransmission of the data may all fail, and the eNB may receive only thedata of a specific UE depending on the location or transmission power ofthe UEs. In the latter case, all of the two or more UEs assume that thetransmission of their data was successful, and thus the eNB has tonotify UEs that have failed in the contention of information about thefailure. That is, providing notification of information about thefailure or success of the contention is called a collision resolution.

A collision resolution method includes two methods. One method is amethod using a collision resolution timer, and the other method is amethod of sending the identity of a UE that was successful in acontention to other UEs. The former method is used when a UE already hasa unique C-RNTI prior to a random access process. That is, the UE thathas already had the C-RNTI sends data, including its own C-RNTI, to aneNB in response to a random access response, and drives a collisionresolution timer. Furthermore, when PDCCH information indicated by itsown C-RNTI is received before the collision resolution timer expires,the UE determines that it was successful in the contention and normallyterminates the random access. In contrast, if the UE does not receive aPDCCH indicated by its own C-RNTI before the collision resolution timerexpires, the UE determines that it failed in the contention and mayperform a random access process again or may notify a higher layer ofthe failure of the contention. In the latter method of the twocontention resolution methods, that is, the method of sending theidentity of a successful UE, is used if a UE does not have a unique cellidentity prior to a random access process. That is, if the UE does nothave its own cell identity, the UE includes an identity (or an S-TMSI ora random number) higher than the cell identity in data based on UL grantinformation included in a random access response, sends the data, anddrives a collision resolution timer. If data including its own higheridentity is transmitted through a DL-SCH before the collision resolutiontimer expires, the UE determines that the random access process wassuccessful. In contrast, if data including its own higher identity isnot received through a DL-SCH before the collision resolution timerexpires, the UE determines that the random access process has failed.

Unlike in the contention-based random access procedure shown in FIG. 8,the operation in the non-contention-based random access procedure isterminated by only the transmission of the first message and the secondmessage. In this case, before a UE sends a random access preamble to aneNB as the first message, the eNB allocates the random access preambleto the UE, and the UE sends the allocated random access preamble to theeNB as the first message and receives a random access response from theeNB. Accordingly, the random connection procedure is terminated.

Reference Signal (RS)

In the wireless communication system, since the data is transmittedthrough the radio channel, the signal may be distorted duringtransmission. In order for the receiver side to accurately receive thedistorted signal, the distortion of the received signal needs to becorrected by using channel information. In order to detect the channelinformation, a signal transmitting method know by both the transmitterside and the receiver side and a method for detecting the channelinformation by using an distortion degree when the signal is transmittedthrough the channel are primarily used. The aforementioned signal isreferred to as a pilot signal or a reference signal (RS).

Recently, when packets are transmitted in most of mobile communicationsystems, multiple transmitting antennas and multiple receiving antennasare adopted to increase transceiving efficiency rather than a singletransmitting antenna and a single receiving antenna. When the data istransmitted and received by using the MIMO antenna, a channel statebetween the transmitting antenna and the receiving antenna need to bedetected in order to accurately receive the signal. Therefore, therespective transmitting antennas need to have individual referencesignals.

Reference signal in a wireless communication system can be mainlycategorized into two types. In particular, there are a reference signalfor the purpose of channel information acquisition and a referencesignal used for data demodulation. Since the object of the formerreference signal is to enable a UE (user equipment) to acquire a channelinformation in DL (downlink), the former reference signal should betransmitted on broadband. And, even if the UE does not receive DL datain a specific subframe, it should perform a channel measurement byreceiving the corresponding reference signal. Moreover, thecorresponding reference signal can be used for a measurement formobility management of a handover or the like. The latter referencesignal is the reference signal transmitted together when a base stationtransmits DL data. If a UE receives the corresponding reference signal,the UE can perform channel estimation, thereby demodulating data. And,the corresponding reference signal should be transmitted in a datatransmitted region.

The DL reference signals are categorized into a common reference signal(CRS) shared by all terminals for an acquisition of information on achannel state and a measurement associated with a handover or the likeand a dedicated reference signal (DRS) used for a data demodulation fora specific terminal. Information for demodulation and channelmeasurement may be provided by using the reference signals. That is, theDRS is used only for data demodulation only, while the CRS is used fortwo kinds of purposes including channel information acquisition and datademodulation.

The receiver side (that is, terminal) measures the channel state fromthe CRS and feeds back the indicators associated with the channelquality, such as the channel quality indicator (CQI), the precodingmatrix index (PMI), and/or the rank indicator (RI) to the transmittingside (that is, base station). The CRS is also referred to as acell-specific RS. On the contrary, a reference signal associated with afeed-back of channel state information (CSI) may be defined as CSI-RS.

The DRS may be transmitted through resource elements when datademodulation on the PDSCH is required. The terminal may receive whetherthe DRS is present through the upper layer and is valid only when thecorresponding PDSCH is mapped. The DRS may be referred to as theUE-specific RS or the demodulation RS (DMRS).

FIG. 9 illustrates a reference signal pattern mapped to a downlinkresource block pair in the wireless communication system to which thepresent invention can be applied.

Referring to FIG. 9, as a unit in which the reference signal is mapped,the downlink resource block pair may be expressed by one subframe in thetimedomain×12 subcarriers in the frequency domain. That is, one resourceblock pair has a length of 14 OFDM symbols in the case of a normalcyclic prefix (CP) (FIG. 9a ) and a length of 12 OFDM symbols in thecase of an extended cyclic prefix (CP) (FIG. 9b ). Resource elements(REs) represented as ‘0’, ‘1’, ‘2’, and ‘3’ in a resource block latticemean the positions of the CRSs of antenna port indexes ‘0’, ‘1’, ‘2’,and ‘3’, respectively and resource elements represented as ‘D’ means theposition of the DRS.

Hereinafter, when the CRS is described in more detail, the CRS is usedto estimate a channel of a physical antenna and distributed in a wholefrequency band as the reference signal which may be commonly received byall terminals positioned in the cell. That is, the CRS is transmitted ineach subframe across a broadband as a cell-specific signal. Further, theCRS may be used for the channel quality information (CSI) and datademodulation.

The CRS is defined as various formats according to an antenna array atthe transmitter side (base station). The RSs are transmitted based onmaximum 4 antenna ports depending on the number of transmitting antennasof a base station in the 3GPP LTE system (for example, release-8). Thetransmitter side has three types of antenna arrays of three singletransmitting antennas, two transmitting antennas, and four transmittingantennas. For instance, in case that the number of the transmittingantennas of the base station is 2, CRSs for antenna #1 and antenna #2are transmitted. For another instance, in case that the number of thetransmitting antennas of the base station is 4, CRSs for antennas #1 to#4 are transmitted.

When the base station uses the single transmitting antenna, a referencesignal for a single antenna port is arrayed.

When the base station uses two transmitting antennas, reference signalsfor two transmitting antenna ports are arrayed by using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated to the reference signals for two antenna portswhich are distinguished from each other.

Moreover, when the base station uses four transmitting antennas,reference signals for four transmitting antenna ports are arrayed byusing the TDM and/or FDM scheme. Channel information measured by adownlink signal receiving side (terminal) may be used to demodulate datatransmitted by using a transmission scheme such as single transmittingantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing, or multi-user MIMO.

In the case where the MIMO antenna is supported, when the referencesignal is transmitted from a specific antenna port, the reference signalis transmitted to the positions of specific resource elements accordingto a pattern of the reference signal and not transmitted to thepositions of the specific resource elements for another antenna port.That is, reference signals among different antennas are not duplicatedwith each other.

The DRS is described in more detail below. The DRS is used to demodulatedata. Precoding weight used for a specific UE in MIMO antennatransmission is used without any change in order for a UE to estimate acorresponding channel in association with a transport channeltransmitted in each transmission antenna when the UE receives areference signal.

The 3GPP LTE system (e.g., Release-8) supports up to a maximum of fourtransmission antennas, and a DRA for rank 1 beamforming is defined. TheDRS for rank 1 beamforming further indicates a reference signal anantenna port index 5.

The LTE-A system which is an evolved version of the LTE system shouldsupport maximum eight transmitting antennas for downlink transmission.Accordingly, reference signals for maximum eight transmitting antennasshould also be supported. In the LTE system, since the downlinkreference signals are defined for maximum four antenna ports, if thebase station includes four or more downlink transmitting antennas andmaximum eight downlink transmitting antennas in the LTE-A system, thereference signals for these antenna ports should be definedadditionally. The reference signals for maximum eight transmittingantenna ports should be designed for two types of reference signals,i.e., the reference signal for channel measurement and the referencesignal for data demodulation.

One of important considerations in designing the LTE-A system is thebackward compatibility. That is, the backward compatibility means thatthe LTE user equipment should be operated normally even in the LTE-Asystem without any problem and the LTE-A system should also support suchnormal operation. In view of reference signal transmission, thereference signals for maximum eight transmitting antenna ports should bedefined additionally in the time-frequency domain to which CRS definedin the LTE is transmitted on full band of each subframe. However, in theLTE-A system, if reference signal patterns for maximum eighttransmitting antennas are added to full band per subframe in the samemanner as the CRS of the existing LTE system, the RS overhead becomestoo great.

Accordingly, the reference signal designed newly in the LTE-A system maybe divided into two types. Examples of the two types of referencesignals include a channel state information-reference signal (CSI-RS)(or may be referred to as channel state indication-RS) for channelmeasurement for selection of modulation and coding scheme (MCS) and aprecoding matrix index (PMI), and a data demodulation-reference signal(DM-RS) for demodulation of data transmitted to eight transmittingantennas.

The CSI-RS for the channel measurement purpose is designed for channelmeasurement mainly unlike the existing CRS used for channel measurement,handover measurement, and data demodulation. The CSI-RS may also be usedfor handover measurement. Since the CSI-RS is transmitted only to obtainchannel state information, it may not be transmitted per subframe unlikethe CRS of the existing LTE system. Accordingly, in order to reduceoverhead, the CSI-RS may intermittently be transmitted on the time axis.

The DM-RS is dedicatedly transmitted to the UE which is scheduled in thecorresponding time-frequency domain for data demodulation. In otherwords, the DM-RS of a specific UE is only transmitted to the regionwhere the corresponding user equipment is scheduled, i.e., thetime-frequency domain that receives data.

In the LTE-A system, an eNB should transmit the CSI-RSs for all theantenna ports. Since the transmission of CSI-RSs for up to eighttransmission antenna ports in every subframe leads to too much overhead,the CSI-RSs should be transmitted intermittently along the time axis,thereby reducing CSI-RS overhead. Therefore, the CSI-RSs may betransmitted periodically at every integer multiple of one subframe, orin a predetermined transmission pattern. The CSI-RS transmission periodor pattern of the CSI-RSs may be configured by the eNB.

In order to measure the CSI-RSs, a UE should have knowledge of theinformation for each of the CSI-RS antenna ports in the cell to whichthe UE belong such as the transmission subframe index, thetime-frequency position of the CSI-RS resource element (RE) in thetransmission subframe, the CSI-RS sequence, and the like.

In the LTE-A system, an eNB should transmit each of the CSI-RSs formaximum eight antenna ports, respectively. The resources used fortransmitting the CSI-RS of different antenna ports should be orthogonal.When an eNB transmits the CSI-RS for different antenna ports, by mappingthe CSI-RS for each of the antenna ports to different REs, the resourcesmay be orthogonally allocated in the FDM/TDM scheme. Otherwise, theCSI-RSs for different antenna ports may be transmitted in the CDM schemewith being mapped to the mutually orthogonal codes.

When an eNB notifies the information of the CSI-RS to the UE in its owncell, the information of the time-frequency in which the CSI-RS for eachantenna port is mapped should be notified. Particularly, the informationincludes the subframe numbers on which the CSI-RS is transmitted, theperiod of the CSI-RS being transmitted, the subframe offset in which theCSI-RS is transmitted, the OFDM symbol number in which the CSI-RS RE ofa specific antenna is transmitted, the frequency spacing, the offset orshift value of RE on the frequency axis.

The CSI-RS is transmitted through 1, 2, 4 or 8 antenna ports. In thiscase, the antenna port which is used is p=15, p=15,16, p=15, . . . , 18,or p=15, . . . , 22. The CSI-RS may be defined only for the subcarrierinterval Δf=15 kHz.

(k′, l′) (herein, k′ is a subcarrier index in a resource block, and l′represents an OFDM symbol index in a slot) and the condition of n_(s) isdetermined according to the CSI-RS configuration shown in Table 3 orTable 4 below.

Table 3 exemplifies the mapping of (k′, l′) according to the CSI-RSconfiguration for the normal CP.

TABLE 3 CSI reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure type 1 and 2 0 (9, 5) 0 (9, 5) 0 (9, 5)0 1 (11, 2)  1 (11, 2)  1 (11, 2)  1 2 (9, 2) 1 (9, 2) 1 (9, 2) 1 3 (7,2) 1 (7, 2) 1 (7, 2) 1 4 (9, 5) 1 (9, 5) 1 (9, 5) 1 5 (8, 5) 0 (8, 5) 06 (10, 2)  1 (10, 2)  1 7 (8, 2) 1 (8, 2) 1 8 (6, 2) 1 (6, 2) 1 9 (8, 5)1 (8, 5) 1 10 (3, 5) 0 11 (2, 5) 0 12 (5, 2) 1 13 (4, 2) 1 14 (3, 2) 115 (2, 2) 1 16 (1, 2) 1 17 (0, 2) 1 18 (3, 5) 1 19 (2, 5) 1 Frame 20(11, 1)  1 (11, 1)  1 (11, 1)  1 21 (9, 1) 1 (9, 1) 1 (9, 1) 1 22 (7, 1)1 (7, 1) 1 (7, 1) 1 23 (10, 1)  1 (10, 1)  1 24 (8, 1) 1 (8, 1) 1 25(6, 1) 1 (6, 1) 1 26 (5, 1) 1 27 (4, 1) 1 28 (3, 1) 1 29 (2, 1) 1 30(1, 1) 1 31 (0, 1) 1

Table 4 exemplifies the mapping of (k′, l′) according to the CSI-RSconfiguration for the extended CP.

TABLE 4 CSI reference Number of CSI reference signals configured signal1 or 2 4 8 configuration (k′, l′) n_(s) mod 2 (k′, l′) n_(s) mod 2 (k′,l′) n_(s) mod 2 Frame structure type 1 and 2 0 (11, 4)  0 (11, 4)  0(11, 4)  0 1 (9, 4) 0 (9, 4) 0 (9, 4) 0 2 (10, 4)  1 (10, 4)  1 (10, 4) 1 3 (9, 4) 1 (9, 4) 1 (9, 4) 1 4 (5, 4) 0 (5, 4) 0 5 (3, 4) 0 (3, 4) 0 6(4, 4) 1 (4, 4) 1 7 (3, 4) 1 (3, 4) 1 8 (8, 4) 0 9 (6, 4) 0 10 (2, 4) 011 (0, 4) 0 12 (7, 4) 1 13 (6, 4) 1 14 (1, 4) 1 15 (0, 4) 1 Framestructure type 2 only 16 (11, 1)  1 (11, 1)  1 (11, 1)  1 17 (10, 1)  1(10, 1)  1 (10, 1)  1 18 (9, 1) 1 (9, 1) 1 (9, 1) 1 19 (5, 1) 1 (5, 1) 120 (4, 1) 1 (4, 1) 1 21 (3, 1) 1 (3, 1) 1 22 (8, 1) 1 23 (7, 1) 1 24(6, 1) 1 25 (2, 1) 1 26 (1, 1) 1 27 (0, 1) 1

Referring to Table 3 and Table 4, for the CSI-RS transmission, in orderto decrease the inter-cell interference (ICI) in the multi-cellenvironment including the heterogeneous network (HetNet) environment,different configurations of maximum 32 (in the case of normal CP) ormaximum 28 (in the case of extended CP) are defined.

The CSI-RS configuration is different depending on the number of antennaports in a cell and the CP, neighbor cells may have differentconfigurations to the maximum. In addition, the CSI-RS configuration maybe divided into the case of being applied to both the FDD frame and theTDD frame and the case of being applied to only the TDD frame.

Based on Table 3 and Table 4, (k′, l′) and n_(s) are determinedaccording to the CSI-RS configuration. By applying these values toEquation 19, the time-frequency resource that each CSI-RS antenna portuses for transmitting the CSI-RS is determined.

FIG. 10 is a diagram illustrating the CSI-RS configuration in a wirelesscommunication system to which the present invention may be applied.

FIG. 10(a) shows twenty CSI-RS configurations that are usable in theCSI-RS transmission through one or two CSI-RS antenna ports, and FIG.10(b) shows ten CSI-RS configurations that are usable by four CSI-RSantenna ports. FIG. 10(c) shows five CSI-RS configurations that areusable in the CSI-RS transmission through eight CSI-RS antenna ports.

As such, according to each CSI-RS configuration, the radio resource(i.e., RE pair) in which the CSI-RS is transmitted is determined.

When one or two CSI-RS antenna ports are configured for transmitting theCSI-RS for a specific cell, the CSI-RS is transmitted on the radioresource according to the configured CSI-RS configuration among twentyCSI-RS configurations shown in FIG. 10(a).

Similarly, when four CSI-RS antenna ports are configured fortransmitting the CSI-RS for a specific cell, the CSI-RS is transmittedon the radio resource according to the configured CSI-RS configurationamong ten CSI-RS configurations shown in FIG. 10(b). In addition, wheneight CSI-RS antenna ports are configured for transmitting the CSI-RSfor a specific cell, the CSI-RS is transmitted on the radio resourceaccording to the configured CSI-RS configuration among five CSI-RSconfigurations shown in FIG. 10(c).

The CSI-RS for each of the antenna ports is transmitted with being CDMto the same radio resource for each of two antenna ports (i.e., {15,16},{17,18}, {19,20}, {21,22}). As an example of antenna ports 15 and 16,although the respective CSI-RS complex symbols are the same for antennaports 15 and 16, the CSI-RS complex symbols are mapped to the same radioresource with being multiplied by different orthogonal codes (e.g.,Walsh code). To the complex symbol of the CSI-RS for antenna port 15,[1, 1] is multiplied, and [1, −1] is multiplied to the complex symbol ofthe CSI-RS for antenna port 16, and the complex symbols are mapped tothe same radio resource. This procedure is the same for antenna ports{17,18}, {19,20} and {21,22}.

A UE may detect the CSI-RS for a specific antenna port by multiplying acode multiplied by the transmitted code. That is, in order to detect theCSI-RS for antenna port 15, the multiplied code [1 1] is multiplied, andin order to detect the CSI-RS for antenna port 16, the multiplied code[1 −1] is multiplied.

Referring to FIGS. 10(a) to (c), when a radio resource is correspondingto the same CSI-RS configuration index, the radio resource according tothe CSI-RS configuration including a large number of antenna portsincludes the radio resource according to the CSI-RS configurationincluding a small number of antenna ports. For example, in the case ofCSI-RS configuration 0, the radio resource for eight antenna portsincludes all of the radio resource for four antenna ports and one or twoantenna ports.

A plurality of CSI-RS configurations may be used in a cell. Zero or oneCSI-RS configuration may be used for the non-zero power (NZP) CSI-RS,and zero or several CSI-RS configurations may be used for the zero powerCSI-RS.

A UE presumes the zero power transmission for the REs (except the caseof being overlapped with the RE that presumes the NZP CSI-RS that isconfigured by a high layer) that corresponds to four CSI-RS column inTable 3 and Table 4 above, for every bit that is configured as ‘1’ inthe Zero Power CSI-RS (ZP-CSI-RS) which is the bitmap of 16 bitsconfigured by a high layer. The Most Significant Bit (MSB) correspondsto the lowest CSI-RS configuration index, and the next bit in the bitmapcorresponds to the next CSI-RS configuration index in order.

The CSI-RS is transmitted in the downlink slot only that satisfies thecondition of n_(s) mod 2 in Table 3 and Table 4 above and the CSI-RSsubframe configuration.

In the case of frame structure type 2 (TDD), in the subframe thatcollides with a special subframe, SS, PBCH or SIB 1(SystemInformationBlockType1) message transmission or the subframe thatis configured to transmit a paging message, the CSI-RS is nottransmitted.

In addition, the RE in which the CSI-RS for a certain antenna port thatis belonged to an antenna port set S (S={15}, S={15,16}, S={17,18},S={19,20} or S={21,22}) is transmitted is not used for transmitting thePDSCH or the CSI-RS of another antenna port.

Since the time-frequency resources used for transmitting the CSI-RS isunable to be used for transmitting data, the data throughput decreasesas the CSI-RS overhead increases. Considering this, the CSI-RS is notconfigured to be transmitted in every subframe, but configured to betransmitted in a certain transmission period that corresponds to aplurality of subframes. In this case, the CSI-RS transmission overheadmay be significantly decreased in comparison with the case that theCSI-RS is transmitted in every subframe.

The subframe period (hereinafter, referred to as ‘CSI-RS transmissionperiod’; T_(CSI-RS)) for transmitting the CSI-RS and the subframe offset(Δ_(CSI-RS)) are represented in Table 5 below.

Table 5 exemplifies the configuration of CSI-RS subframe.

TABLE 5 CSI-RS periodicity CSI-RS subframe CSI-RS-SubframeConfigT_(CSI-RS) offset Δ_(CSI-RS) I_(CSI-RS) (subframes) (subframes) 0-4 5I_(CSI-RS)  5-14 10 I_(CSI-RS) − 5  15-34 20 I_(CSI-RS) − 15 35-74 40I_(CSI-RS) − 35  75-154 80 I_(CSI-RS) − 75

Referring to Table 5, according to the CSI-RS subframe configuration(I_(CSI-RS)), the CSI-RS transmission period (T_(CSI-RS)) and thesubframe offset (Δ_(CSI-RS)) are determined.

The CSI-RS subframe configuration in Table 5 is configured as one of the‘SubframeConfig’ field and the ‘zeroTxPowerSubframeConfig’ field inTable 2 above. The CSI-RS subframe configuration may be separatelyconfigured for the NZP CSI-RS and the ZP CSI-RS.

The subframe including the CSI-RS satisfies Equation 12 below.

(10n _(f) +└n _(s)/2┘−Δ_(CSI-RS))mod T _(CSI-RS)=0  [Equation 12]

In Equation 12, T_(CSI-RS) represents the CSI-RS transmission period,ΔCSI-RS represents the subframe offset value, n_(f) represents thesystem frame number, and n_(s) represents the slot number.

In the case of a UE in which transmission mode 9 is set for a servingcell, a single CSI-RS resource may be configured in the UE. In the caseof a UE in which transmission mode 10 is set for a serving cell, one ormore CSI-RS resources may be configured in the UE.

For each CSI-RS resource configuration, the following parameters may beset through high layer signaling.

-   -   If transmission mode 10 is set, the CSI-RS resource        configuration identifier    -   The number of CSI-RS ports    -   The CSI-RS configuration (refer to Table 3 and Table 4)    -   The CSI-RS subframe configuration (I_(CSI-RS); refer to Table 5)    -   If transmission mode 9 is set, the transmission power (P_(c))        for the CSI feedback    -   If transmission mode 10 is set, the transmission power (P_(c))        for the CSI feedback with respect to each CSI process. When the        CSI subframe sets C_(CSI,0) and C_(CSI,1) are set by a high        layer for the CSI process, P_(c) is set in each CSI subframe set        of the CSI process.    -   The pseudo-random sequence generator parameter (n_(ID))    -   If transmission mode 10 is set, the QCL scrambling identifier        (qcl-ScramblingIdentity-r11) for assuming the Quasi Co-Located        (QCL) type B UE, the CRS port count (crs-PortsCount-r11), and        the high layer parameter (‘qcl-CRS-Info-r11’) that includes the        MBSFN subframe configuration list (mbsfn-SubframeConfigList-r11)        parameter.

When the CSI feedback value obtained by a UE has the value in the rangeof [−8, 15] dB, P_(c) is presumed by the ratio of the PDSCH EPRE for theCSI-RS EPRE. Herein, the PDSCH EPRE corresponds to the symbol in whichthe ratio of PDSCH EPRE for the CRS EPRE is ρ_(A).

In the same subframe of a serving cell, the CSI-RS and the PMCH are notconfigured together.

When four CRS antenna ports are configured in frame structure type 2,the CSI-RS configuration index belonged to [20-31] set in the case ofthe normal CP (refer to Table 3) or [16-27] set in the case of theextended CP (refer to Table 4) is not configured to a UE.

A UE may assume that the CSI-RS antenna port of the CSI-RS resourceconfiguration has the QCL relation with the delay spread, the Dopplerspread, the Doppler shift, the average gain and the average delay.

The UE to which transmission mode 10 and QCL type B are configured mayassume that the antenna ports 0 to 3 corresponding to the CSI-RSresource configuration and the antenna ports 15 to 22 corresponding tothe CSI-RS resource configuration have the QCL relation with the Dopplerspread and the Doppler shift.

For the UE to which transmission mode 10 is configured, one or moreChannel-State Information-Interference Measurement (CSI-IM) resourceconfiguration may be set.

The following parameters may be configured for each CSI-IM resourceconfiguration through high layer signaling.

-   -   The ZP CSI-RS configuration (refer to Table 3 and Table 4)    -   The ZP CSI-RS subframe configuration (I_(CSI-RS); refer to Table        5)

The CSI-IM resource configuration is the same as one of the configuredZP CSI-RS resource configuration.

In the same subframe in a serving cell, the CSI-IM resource and the PMCHare not configured simultaneously.

For a UE in which transmission modes 1 to 9 are set, a ZP CSI-RSresource configuration may be configured in the UE for a serving cell.For a UE in which transmission mode 10 is set, one or more ZP CSI-RSresource configurations may be configured in the UE for the servingcell.

The following parameters may be configured for the ZP CSI-RS resourceconfiguration through high layer signaling.

-   -   The ZP CSI-RS configuration list (refer to Table 3 and Table 4)    -   The ZP CSI-RS subframe configuration (I_(CSI-RS); refer to Table        5)

In the same subframe in a serving cell, the ZP CSI-RS resource and thePMCH are not configured simultaneously.

Cell Measurement/Measurement Report

For one or several methods among the several methods (handover, randomaccess, cell search, etc.) for guaranteeing the mobility of UE, the UEreports the result of a cell measurement to an eNB (or network).

In the 3GPP LTE/LTE-A system, the cell-specific reference signal (CRS)is transmitted through 0, 4, 7 and 11^(th) OFDM symbols in each subframeon the time axis, and used for the cell measurement basically. That is,a UE performs the cell measurement using the CRS that is received from aserving cell and a neighbor cell, respectively.

The cell measurement is the concept that includes the Radio resourcemanagement (RRM) measurement such as the Reference signal receive power(RSRP) that measures the signal strength of the serving cell and theneighbor cell or the signal strength in comparison with total receptionpower, and so on, the Received signal strength indicator (RSSI), theReference signal received quality (RSRQ), and the like and the RadioLink Monitoring (RLM) measurement that may evaluate the radio linkfailure by measuring the link quality from the serving cell.

The RSRP is a linear average of the power distribution of the RE inwhich the CRS is transmitted in a measurement frequency band. In orderto determine the RSRP, CRS (R0) that corresponds to antenna port ‘0’ maybe used. In addition, in order to determine the RSRP, CRS (R1) thatcorresponds to antenna port ‘1’ may be additionally used. The number ofREs used in the measurement frequency band and the measurement durationby a UE in order to determine the RSRP may be determined by the UEwithin the limit that satisfies the corresponding measurement accuracyrequirements. In addition, the power per RE may be determined by theenergy received in the remaining part of the symbol except the CP.

The RSSI is obtained as the linear average of the total reception powerthat is detected from all sources including the serving cell and thenon-serving cell of the co-channel, the interference from an adjacentchannel, the thermal noise, and so on by the corresponding UE in theOFDM symbols including the RS that corresponds to antenna port ‘0’. Whena specific subframe is indicated by high layer signaling for performingthe RSRQ measurement, the RSSI is measured through all OFDM symbols inthe indicated subframes.

The RSRQ is obtained by N×RSRP/RSSI. Herein, N means the number of RBsof the RSSI measurement bandwidth. In addition, the measurement of thenumerator and the denominator in the above numerical expression may beobtained by the same RB set.

A BS may forward the configuration information for the measurement to aUE through high layer signaling (e.g., RRC Connection Reconfigurationmessage).

The RRC Connection Reconfiguration message includes a radio resourceconfiguration dedicated (‘radioResourceConfigDedicated’) InformationElement (IE) and the measurement configuration (‘measConfig’) IE.

The ‘measConfig’ IE specifies the measurement that should be performedby the UE, and includes the configuration information for theintra-frequency mobility, the inter-frequency mobility, the inter-RATmobility as well as the configuration of the measurement gap.

Particularly, the ‘measConfig’ IE includes ‘measObjectToRemoveList’ thatrepresents the list of the measurement object (‘measObject’) that is tobe removed from the measurement and ‘measObjectToAddModList’ thatrepresents the list that is going to be newly added or amended. Inaddition, ‘MeasObjectCDMA2000’, ‘MeasObjctEUTRA’, ‘MeasObjectGERAN’ andso on are included in the ‘measObject’ according to the communicationtechnique.

The ‘RadioResourceConfigDedicated’ IE is used to setup/modify/releasethe Radio Bearer, to change the MAC main configuration, to change theSemi-Persistent Scheduling (SPS) configuration and to change thededicated physical configuration.

The ‘RadioResourceConfigDedicated’ IE includes the‘measSubframePattern-Sere’ field that indicates the time domainmeasurement resource restriction pattern for serving cell measurement.In addition, the ‘RadioResourceConfigDedicated’ IE includes‘measSubframeCellList’ indicating the neighbor cell that is going to bemeasured by the UE and ‘measSubframePattern-Neigh’ indicating the timedomain measurement resource restriction pattern for neighbor cellmeasurement.

The time domain measurement resource restriction pattern that isconfigured for the measuring cell (including the serving cell and theneighbor cell) may indicate at least one subframe per radio frame forperforming the RSRQ measurement. The RSRQ measurement is performed onlyfor the subframe indicated by the time domain measurement resourcerestriction pattern that is configured for the measuring cell.

As such, a UE (e.g., 3GPP Rel-10) should measure the RSRQ only in theduration configured by the subframe pattern (‘measSubframePattern-Serv’)for the serving cell measurement and the subframe pattern(‘measSubframePattern-Neigh’) for the neighbor cell measurement.

Although the measurement in the pattern for the RSRQ is not limited, butit is preferable to be measured only in the pattern for the accuracyrequirement.

Quasi Co-Located (QCL) Between Antenna Ports

Quasi co-located and quasi co-location (QC/QCL) may be defined asfollows.

If two antenna ports have a QC/QCL relation (or subjected to QC/QCL), aUE may assume that the large-scale property of a signal transferredthrough one antenna port may be inferred from a signal transferredthrough the other antenna port. In this case, the large-scale propertyincludes one or more of delay spread, Doppler spread, a frequency shift,average received power, and reception timing.

Furthermore, the following may be defined. Assuming that two antennaports have a QC/QCL relation (or subjected to QC/QCL), a UE may assumethat the large-scale property of a channel transferred through oneantenna port may be inferred from a wireless channel transferred throughthe other antenna port. In this case, the large-scale property includesone or more of delay spread, Doppler spread, Doppler shift, an averagegain, and average delay.

That is, if two antenna ports have a QC/QCL relation (or subjected toQC/QCL), it means that the large-scale property of a wireless channelfrom one antenna port is the same as the large-scale property of awireless channel from the other antenna port. Assuming that a pluralityof antenna ports in which an RS is transmitted is taken intoconsideration, if antenna ports on which two types of different RSs aretransmitted have a QCL relation, the large-scale property of a wirelesschannel from one antenna port may be replaced with the large-scaleproperty of a wireless channel from the other antenna port.

In this specification, the QC/QCL-related definitions are notdistinguished. That is, the QC/QCL concept may comply with one of thedefinitions. In a similar other form, the QC/QCL concept definition maybe changed in a form in which antenna ports having an established QC/QCLassumption may be assumed to be transmitted at the same location (i.e.,co-location) (e.g., a UE may assume antenna ports to be antenna portstransmitted at the same transmission point). The spirit of the presentinvention includes such similar modifications. In an embodiment of thepresent invention, the QC/QCL-related definitions are interchangeablyused, for convenience of description.

In accordance with the concept of the QC/QCL, a UE may not assume thesame large-scale property between wireless channels from correspondingantenna ports with respect to non-QC/QCL antenna ports. That is, in thiscase, a UE may perform independent processing on timing acquisition andtracking, frequency offset estimation and compensation, delayestimation, and Doppler estimation for each configured non-QC/QCLantenna port.

There are advantages in that a UE can perform the following operationsbetween antenna ports capable of an assuming QC/QCL:

-   -   With respect to delay spread and Doppler spread, a UE may        identically apply the results of a power-delay profile, delay        spread and a Doppler spectrum, and Doppler spread estimation for        a wireless channel from any one antenna port to a Wiener filter        which is used upon channel estimation for a wireless channel        from other antenna ports.    -   With respect to a frequency shift and received timing, a UE may        perform time and frequency synchronization on any one antenna        port and then apply the same synchronization to the demodulation        of other antenna ports.    -   With respect to average received power, a UE may average        reference signal received power (RSRP) measurement for two or        more antenna ports.

For example, if a DMRS antenna port for downlink data channeldemodulation has been subjected to QC/QCL with the CRS antenna port of aserving cell, a UE may apply the large-scale property of a wirelesschannel, estimated from its own CRS antenna port upon channel estimationthrough the corresponding DMRS antenna port, in the same manner, therebyimproving reception performance of a DMRS-based downlink data channel.

The reason for this is that an estimation value regarding a large-scaleproperty can be more stably obtained from a CRS because the CRS is areference signal that is broadcasted with relatively high density everysubframe and in a full bandwidth. In contrast, a DMRS is transmitted ina UE-specific manner with respect to a specific scheduled RB, and theprecoding matrix of a precoding resource block group (PRG) unit that isused by an eNB for transmission may be changed. Thus, a valid channelreceived by a UE may be changed in a PRG unit. Accordingly, although aplurality of PRGs has been scheduled in the UE, performancedeterioration may occur when the DMRS is used to estimate thelarge-scale property of a wireless channel over a wide band.Furthermore, a CSI-RS may also have a transmission cycle ofseveral˜several tens of ms, and each resource block has also low densityof 1 resource element for each antenna port in average. Accordingly, theCSI-RS may experience performance deterioration if it is used toestimate the large-scale property of a wireless channel.

That is, a UE can perform the detection/reception, channel estimation,and channel state report of a downlink reference signal through a QC/QCLassumption between antenna ports.

Restricted RLM and RRM/CSI Measurement

As one of methods for interference coordination, an aggressor cell mayuse a silent subframe (or may be called an almost blank subframe (ABS))in which the transmission power/activity of partial physical channelsare reduced (in this case, to reduce the transmission power/activity mayinclude an operation for configuring the transmission power/activity tozero power). A victim cell may perform time domain inter-cellinterference coordination for scheduling UE by taking into considerationthe silent subframe.

In this case, from a standpoint of a victim cell UE, an interferencelevel may greatly vary depending on a subframe.

In such a situation, in order to perform a radio resource management(RRM) operation for measuring more accurate radio link monitoring (RLM)or RSRP/RSRQ in each subframe or to measure channel state information(CSI) for link adaptation, the monitoring/measurement may be restrictedto sets of subframes having a uniform interference characteristic. Inthe 3GPP LTE system, restricted RLM and RRM/CSI measurement are definedas follows.

A UE monitors downlink link quality based on a cell-specific referencesignal (CRS) in order to sense downlink link quality of a PCell. The UEestimates downlink radio link quality, and compares the estimate of athreshold Q_out with the estimate of a threshold Q_in order to monitorthe downlink radio link quality of the PCell.

The threshold Q_out is defined as a level at which downlink radio linkcannot be reliably received, and corresponds to a 10% block error rate(BER) of hypothetical PDCCH transmission in which a PCFICH error hasbeen taken into consideration based on transmission parameters listed inTable 6 below.

The threshold Q_in is defined as a level at which downlink radio linkquality can be more significantly reliably received compared to downlinkradio link quality in the threshold Q_out, and corresponds to a 2% BERof hypothetical PDCCH transmission in which a PCFICH error has beentaken into consideration based on transmission parameters listed inTable 7 below.

When higher layer signaling indicates a specific subframe for restrictedRLM, radio link quality is monitored.

Specific requirements are applied when a time domain measurementresource restriction pattern for performing RLM measurement isconfigured by a higher layer and if a time domain measurement resourcerestriction pattern configured for a cell to be measured indicates atleast one subframe per radio frame for performing RLM measurement.

If CRS assistance information is provided, the requirements may besatisfied when the number of transmit antennas of one or more cells towhich CRS assistance information has been provided is different from thenumber of transmit antennas of a cell in which RLM is performed.

If UE is not provided with CRS assistance information or CRS assistancedata is not valid for the entire evaluation period, a time domainmeasurement restriction may be applied when a collision occurs between aCRS and an ABS configured within a non-multicast broadcast singlefrequency network (MBSFN) subframe.

Table 6 illustrates PDCCH/PCFICH transmission parameters in anout-of-sync status.

TABLE 6 ATTRIBUTE VALUE DCI format 1A Number of control OFDM 2;bandwidth ≧ 10 MHz symbols 3; 3 MHz ≦ bandwidth ≦ 10 MHz 4; bandwidth =1.4 MHz Aggregation level (CCE) 4; bandwidth = 1.4 MHz 8; bandwidth ≧ 3MHz Ratio of PDCCH RE energy 4 dB; if a single antenna port is used toaverage RS RE energy for CRS transmission by a PCell 1 dB; if two orfour antenna ports are used for CRS transmission by a PCell Ratio ofPCFICH RE 4 dB; if a single antenna port is used energy to average forCRS transmission by a PCell RS RE energy 1 dB: if two or four antennaports are used for CRS transmission by a PCell

Table 7 illustrates PDCCH/PCFICH transmission parameters in an in-syncstatus.

TABLE 7 ATTRIBUTE VALUE DCI format 1C Number of control OFDM 2;bandwidth ≧ 10 MHz symbols 3; 3 MHz ≦ bandwidth ≦ 10 MHz 4; bandwidth =1.4 MHz Aggregation level (CCE) 4 Ratio of PDCCH RE energy 0 dB; If asingle antenna port is used to average RS RE energy for CRS transmissionby a PCell −3 dB; If two or four antenna ports are used for CRStransmission by a PCell Ratio of PCFICH RE 4 dB; If a single antennaport is used energy to average for CRS transmission by a PCell RS REenergy 1 dB; If two or four antenna ports are used for CRS transmissionby a PCell

Downlink radio link quality for a PCell is monitored by a UE in order toindicate the out-of-sync status/in-sync status in a higher layer.

In a non-DRX mode operation, a physical layer of a UE assesses radiolink quality evaluated for a previous time interval by taking intoconsideration thresholds Q_out and Q_in in each radio frame.

If higher layer signaling indicates a specific subframe for restrictedRLM, the measurement of radio link quality is not performed in othersubframes not indicated in the higher layer signaling.

If radio link quality is poorer than the threshold Q_out, the physicallayer of a UE indicates the out-of-sync status for a higher layer withina radio frame whose radio link quality was measured. If the radio linkquality is better than the threshold Q_in, the physical layer of the UEindicates the in-sync status for the higher layer within a radio framewhose radio link quality was measured.

Massive MIMO

In a wireless communication system after LTE Release (Rel)-12, theintroduction of an active antenna system (AAS) is taken intoconsideration.

Unlike in an existing passive antenna system in which an amplifier andan antenna in which the phase and size of a signal can be adjusted havebeen separated, the AAS means a system in which each antenna isconfigured to include an active element, such as an amplifier.

The AAS does not require a separate cable, a connector, and otherhardware for connecting an amplifier and an antenna depending on use ofan active antenna and thus has high efficiency in terms of energy and anoperation cost. In particular, the AAS enables an advanced MIMOtechnology, such as the forming of an accurate beam pattern or 3-D beampattern in which a beam direction and a beam width have been taken intoconsideration, because the AAS supports an electronic beam controlmethod for each antenna.

Due to the introduction of an advanced antenna system, such as the AAS,a massive MIMO structure including a plurality of input/output antennasand a multi-dimensional antenna structure is also taken intoconsideration. For example, unlike in an existing straight-line antennaarray, if a 2-D antenna array is formed, a 3-D beam pattern may beformed by the active antenna of the AAS. If a 3-D beam pattern is usedfrom a viewpoint of a transmission antenna, the forming of a semi-staticor dynamic beam in the vertical direction of a beam in addition to thehorizontal direction can be performed. For example, an application, suchas the forming of a sector in the vertical direction may be taken intoconsideration.

Furthermore, from a viewpoint of a reception antenna, when a receptionbeam is formed using a massive reception antenna, an effect of a rise ofsignal power according to an antenna array gain may be expected.Accordingly, in the case of uplink, an eNB may receive a signaltransmitted by a UE through a plurality of antennas. In this case, thereis an advantage in that the UE can configure its own transmission powervery low by taking into consideration the gain of a massive receptionantenna in order to reduce an interference influence.

FIG. 11 illustrates a system having a plurality oftransmission/reception antennas through which an eNB or a UE is capableof three-dimensional (3-D) beamforming based on an AAS in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

FIG. 11 is a diagram of the aforementioned example and illustrates a 3DMIMO system using a 2-D antenna array (i.e., a 2D-AAS).

Cell Coverage of Massive MIMO

A multiple antenna system, for example, a system having N transmissionantennas may perform beamforming so that received power is increased bya maximum of N times at a specific point, assuming that totaltransmission power is identically transmitted compared to a singleantenna system.

Even an eNB having multiple antennas, a channel that transfers a CRS, aPSS/SSS, a PBCH and broadcast information does not perform beamformingin a specific direction so that all of UEs within an eNB coverage areacan receive them.

In some cases, a PDSCH, that is, a channel that transfers unicastinformation to a specific UE, performs beamforming according to thelocation of a corresponding UE and link situation in order to improvetransmission efficiency. That is, the transmission data stream of thePDSCH is precoded in order to form a beam in a specific direction andtransmitted through multiple antenna ports. Accordingly, for example, iftransmission power of a CRS and transmission power of a PDSCH are thesame, received power of a precoded PDSCH beamformed toward acorresponding UE may be increased up to a maximum of N times compared toaverage received power of a CRS to a specific UE.

Up to now, in the LTE Rel-11 system, an eNB having a maximum of 8transmission antennas is taken into consideration. This means thatreceived power of a precoded PDSCH may be eight times greater thanaverage received power of a CRS. In the future, however, if the numberof transmission antennas of an eNB is 100 or more due to theintroduction of a massive MIMO system, a difference between receivedpower of a CRS and received power of a precoded PDSCH may be 100 timesor more. In conclusion, due to the introduction of the massive MIMOsystem, the coverage area of a CRS transmitted by a specific eNB and thecoverage area of a DM-RS-based PDSCH are not identical.

In particular, such a phenomenon may be significant if a difference inthe number of transmission antennas between two adjacent eNBs is great.A representative example includes an example in which a macro cellhaving 64 transmission antennas and a micro cell (e.g., a pico cell)having a single transmission antenna neighbor each other. A UE served inan initial deployment process of massive MIMO first expects that thenumber of antennas may be increased from many macro cells. Accordingly,in the case of a heterogeneous network in which a macro cell, a microcell and a pico cell are mixed, there is a great difference in thenumber of transmission antennas between adjacent eNBs.

For example, in the case of a pico cell having a single transmissionantenna, the coverage area of a CRS and the coverage area of a PDSCH arethe same. In the case of a macro cell having 64 transmission antennas,the coverage area of a PDSCH is greater than the coverage area of a CRS.Accordingly, if initial access and handover are determined based on onlyRSRP or RSRQ, that is, reception quality of the CRS, at the boundary ofthe macro cell and a pico cell, an eNB capable of providing the bestquality of the PDSCH may not be selected as a serving cell. As a simplesolution for this problem, PDSCH received power of an eNB having Ntransmission antennas may be assumed to be N times great, but such amethod is not the best solution if a case where the eNB cannot performbeamforming in all of directions as possible is taken intoconsideration.

RRM-RS

This specification proposes a method for sending a precoded referencesignal (RS) and performing RRM measurement on the precoded RS. In thisspecification, a precoded RS for this purpose is hereinafter referred toas an “RRM-RS.” The RRM-RS includes a plurality of antenna ports, andbeamforming is differently configured for each antenna port so that a UEcan measure RSRP for each transmission beam. For example, if an eNB isable to perform beamforming in M directions, an RRM-RS including M portsmay be configured.

Cycling and Multiplexing of RRM-RS

An M-port RRM-RS may be subjected to CDM or classified into FDM/TDM inthe same subframe and transmitted. That is, a transmission signal foreach antenna port of the M-port RRM-RS may be transmitted using adifferent transmission RE in the same subframe. If a transmission signalfor each antenna port of the M-port RRM-RS is transmitted using the sameRE, orthogonal scrambling code may be used between antenna ports inorder to avoid interference between the antenna ports.

In some cases, the number of antenna ports of an RRM-RS which may betransmitted in one subframe at the same time may be set as K, may bedivided into (M/K) subframes, and may be then transmitted.

In this case, the configuration parameter of the RRM-RS includes a totalnumber of antenna ports M and the number of antenna ports K transmittedin one subframe at the same time. The configuration parameter of theRRM-RS also includes an RRM-RS transmission cycle P and an offset O. Inthis case, the RRM-RS transmission cycle is defined as the interval ofsubframes in which an RRM-RS is transmitted. For example, if P=10, O=5,M=64, and K=32, the RRM-RS is transmitted in subframes having subframeindices (SFI) of 5, 15, 25, 35, . . . . In the subframe having SFI=5,No. 31 RRM-RS is transmitted in an antenna port 0. In the subframehaving SFI=15, No. 63 RRM-RS is transmitted in an antenna port 32. Inthe subframe having SFI=25, No. 31 RRM-RS is transmitted again in theantenna port 0.

In some cases, in a method for defining an RRM-RS transmission cycle asthe interval of subframes in which the RS of the same antenna port istransmitted, dividing the antenna ports of an RRM-RS into (M/K)subframes, and sending the antenna ports, the antenna ports are dividedinto (M/K) contiguous subframes and transmitted. For example, if P=20,O=5, M=64, and K=32, an RRM-RS is transmitted in subframes having SFIsof 5, 6, 25, 26, 45, 46, . . . . In the subframe having SFI=5, No. 31RRM-RS is transmitted in an antenna port 0. In the subframe havingSFI=6, No. 63 RRM-RS is transmitted in the antenna port 32. In thesubframe having SFI=25, No. 31 RRM-RS is transmitted again in theantenna port 0.

RSRP Measurement and Report

RSRP of an RRM-RS is measured and reported for each antenna port. Aplurality of RRM-RSs may be configured in a UE.

If each RRM-RS is transmitted by each cell, the configuration of RRM-RSstransmitted by a serving cell and neighboring cells may be designed to aUE. One cell may send a plurality of RRM-RSs. When a UE reports RSRP ofan RRM-RS, it also provides notification that the corresponding RSRPcorresponds to RSRP measurement results of which antenna port of whichRRM-RS.

In order to calculate RSRP of an RRM-RS, reception signal levels ofrespective antenna ports are averaged. A time window in which theaverage is calculated may be designed by an eNB, or RSRP may becalculated by averaging reception signal levels of the antenna ports ofRRM-RSs during a predetermined time (e.g., 200 ms). Alternatively, RSRPmay be calculated by filtering average received power obtained in eachtime window again.

A UE in which a plurality of RRM-RSs has been configured measures RSRPof each antenna port of each of the RRM-RSs. If R RRM-RSs have beenconfigured in a UE and the number of antenna ports of an r-th RRM-RS isM_r, RSRP of the m-th antenna port of the r-th RRM-RS is defined asRSRP(r,m). The UE aligns the RSRP(r,m), selects RSRP of L antenna portsthat belong to the aligned RSRP(r,m) and that are strongly received, andreports the selected RSRP.

As a slight modification method of the aforementioned method, a UEaligns RSRP(r,m), selects RSRP of antenna ports that belong to thealigned RSRP(r,m) and that are strongly received, and reports onlypieces of RSRP of ports that fall within a specific difference comparedto the RSRP of the selected antenna ports, that is, max(RSRP(r,m)). Thatis, RSRP of a maximum of L antenna ports, which has an RSRP differencegreater than a specific threshold in an RSRP ratio or dB scaleexpression as follows, is reported.

RSRP(r,m)−max(RSRP(r,m))>Threshold  [Equation 13]

For another example, the antenna ports of a precoded CSI-RS configuredin a corresponding UE and an RRM-RS transmitted by a serving cell havinga similar beam direction may be designated as reference antenna ports.If the (m_0)-th antenna port of an (r_0)-th RRM-RS has been designed toa UE as a reference antenna port, the UE reports another antenna port ifa difference between RSRP of another antenna port and RSRP of thereference antenna port falls within a specific difference. That is, theUE reports an antenna port if a difference between pieces of RSRPexceeds a specific threshold in an RSRP ratio or dB scale expression asfollows.

RSRP(r,m)−RSRP(r_0,m_0)>Threshold  [Equation 14]

FIG. 12 illustrates RSRP for each antenna port of an RRM-RS according toan embodiment of the present invention.

FIG. 12 shows an example of RSRP of each antenna port of an RRM-RSincluding 32 antenna ports.

If a UE has been configured to report RSRP of an antenna port havingRSRP of 5 dB or less compared to an antenna port having the greatestRSRP, the UE reports an antenna port having RSRP of more than 35 dBbecause an antenna port 13 has the greatest RSRP of 40 dB as in FIG. 12.That is, RSRP of antenna ports 24, 25 and 26 including the RSRP of theantenna port 13 is reported to an eNB.

Antenna Port Grouping

Beamforming may be differently configured for each antenna port. In thiscase, each antenna port corresponds to each beam.

Accordingly, each antenna port index (i) may be mapped to each beamindex (i). If beams are indexed so that the directions of an (i)-th beamand an (i+1)-th beam are adjacent, as in the example of FIG. 12, RSRPbetween adjacent antenna ports has a similar characteristic. Suchsimilarity is also generated between the (i)-th beam and an (i+c)-thbeam, but is reduced as “c” increases. Whether high similarity isgenerated between some continuous and adjacent beams is determined bythe interval of beams, the width of a beam, and the scattering degree ofmulti-paths.

An eNB that has received a report on RSRP measurement results based onan RRM-RS checks an approximate location of a corresponding UE andnotifies the UE of a precoded CSI-RS configuration transmitted toward acorresponding point so that the U can measure a CSI-RS and feeds backCSI (e.g., an RI, a PMI and a CQI) for PDSCH scheduling. Furthermore, aneNB that has received a report on RSRP measurement results based onRRM-RSs transmitted by a plurality of cells determines that acorresponding UE will be handovered to which cell and which precodedCSI-RS will be configured in the UE in a target cell based on the RSRPmeasurement results. That is, RSRP measurement results based on RRM-RSsprovide an eNB with important information necessary to determine thatwhich precoded CSI-RS will be configured in a corresponding UE in thefuture.

If 4-port CSI-RSs are configured in a corresponding UE based on RSRPmeasurement results, such as that in the example of FIG. 12, so that amaximum of 4 data streams can be transmitted or the best beam switchingis rapidly performed in line with a change of fading, it is expectedthat to generate and configure 4-port CSI-RSs having the same beamdirection as RRM-RS ports 13, 24, 25 and 26 having the greatest RSRPwill be optimal. However, overhead is too great if a CSI-RS isoptimized, generated and transmitted for each UE. Accordingly, a methodfor reducing CSI-RS transmission overhead is to allow many UEs in thesame environment to share a CSI-RS. In order to achieve the aboveobject, CSI-RS antenna ports within one CSI-RS configuration may beprecoded to have a characteristic of a beam transmitted in an adjacentdirection. That is, if a 4-port CSI-RS1 having the same beam directionas RRM-RS ports 12, 13, 14 and 15 and a 4-port CSI-RS2 having the samebeam direction as RRM-RS ports 24, 25, 26 and 27 have been previouslyconfigured by taking into consideration different served UEs, whether itis better to configure which CSI-RS in a corresponding UE may bedetermined based on the RSRP report of an RRM-RS.

In another embodiment of the present invention, RSRP is also measuredand reported with respect to an antenna port group. In the proposedmethod, antenna ports are grouped, and RSRP of an antenna port group iscalculated by averaging pieces of RSRP of antenna ports belonging to thecorresponding antenna port group. The group may be previously determinedor an eNB may provide notification of the group. Alternatively, a UE maydetermine a grouping method and report the determined grouping method.

As in the example of FIG. 12, RRM-RSs including 32 ports may be groupedevery 4 ports. The groups may be disjointed and grouped into 8 (=32/4)groups. In this case, an (i)-th port group includes RRM-RS ports (4i),(4i+1), (4i+2), and (4i+3). RSRP of the (i)-th port group is defined asan average of pieces of RSRP of the antenna ports (4i), (4i+1), (4i+2),and (4i+3).

In yet another embodiment, overlapping between groups may be permitted,and grouping may be performed. If RRM-RSs including 32 ports are groupedevery 4 ports, the RRM-RSs are grouped into 15 groups. In this case, an(i)-th port group includes RRM-RS ports (2i), (2i+1), (2i+2), and(2i+3). If the proposed method is generalized, ports are grouped every Aports and a port interval between adjacent groups is set as B, an (i)-thport group includes RRM-RS ports (B*i), (B*i+1), . . . , (B*i+A−1). AneNB may designate the setting of the parameters A and B to a UE, or a UEmay select the setting of the parameters A and B by taking intoconsideration a channel environment and UE capability and report theselected setting.

As a modification of the proposed method, in a method for selecting anantenna port group to be reported, a UE may take into considerationcapabilities which may be obtained through a corresponding antenna portgroup compared to RSRP. In this case, the UE calculates the capabilitiesby taking into consideration multi-layer data transmission from aplurality of antennas within the antenna port group.

Antenna Port Grouping Level

In the proposed method, a plurality of grouping methods having differentsizes may be used. That is, a method for grouping antenna ports every A1ports and a method for grouping antenna ports every A2 ports may be usedat the same time. A method for grouping antenna ports every A_i ports ishereinafter referred to as a “grouping level i.”

FIG. 13 illustrates RRM-RS antenna port grouping levels according to anembodiment of the present invention.

FIG. 13 shows an example of a grouping method performed by applying a4-step grouping level to 16-port RRM-RSs. In the example, the groupinglevel 1 shows a method of grouping antenna ports every port and shows amethod not performing grouping. Furthermore, antenna ports are groupedevery 2 ports, 4 ports and 8 ports in the grouping levels 2, 3 and 4,respectively. In the example of FIG. 13, antenna port groups having thesame level have been illustrated as being disjointed and configured.

In such a multiple grouping method, a UE reports RSRP for each groupinglevel. That is, a UE selects and reports an antenna group having highRSRP for each grouping level. Alternatively, a UE may compare RSRP ofantenna groups having different levels and report a group level comparedto the best group. In order to compare RSRP between antenna groupshaving different levels 1, group RSRP of each level is corrected by aspecific offset and compared. In the case where R RRM-RSs have beenconfigured, if RSRP of the (g)-th antenna port group of the (l)-thgrouping level of an (r)-th RRM-RS is defined as GRSRP(r,l,g),Adj_GRSRP(r,l,g) is calculated by correcting GRSRP(r,l,g) by anoffset(r,l) designated for the (l)-th grouping level of the (r)-thRRM-RS by an eNB as follows and is compared with GRSRP(r,l,g).

Adj_GRSRP(r,l,g)=GRSRP(r,l,g)+offset(r,l)  [Equation 15]

In addition, in order to reduce a frequent change in the best L reportedin a method for reporting RSRP of the best L port groups for eachgrouping level or in all of grouping methods, RSRP may be corrected byadding a hysteresis parameter Hy.

Adj_GRSRP(r,l,g)=GRSRP(r,l,g)+offset(r,l)±Hy  [Equation 16]

In Equation 16, whether the parameter Hy is to be added or subtracted isdetermined depending on whether a corresponding port group is includedin the best L GRSRP in a previous report. If the corresponding portgroup is included in the best L GRSRP in the previous report, theparameter Hy is added to apply a bias so that high Adj_RSRP is obtained,thereby reducing a frequent change of a port group having the best LAdj_GRSRP.

In a proposed method, a reference antenna port group may be designatedto a UE. An eNB may designate the antenna port groups of a precodedCSI-RS configured in a corresponding UE and an RRM-RS transmitted by aserving cell having the same beam direction as a reference antenna portgroup. A reference antenna port group may be designated in a UE for eachgrouping level. Alternatively, one reference antenna port group may bedesignated in a UE in all of grouping levels. If the (m_0)-th antennaport group of the (l_0)-th grouping level of an (r_0)-th RRM-RS has beendesignated in a UE as a reference antenna port group, the UE performsreporting if Adj_GRSRP of another antenna port group exceeds a specificthreshold compared to Adj_GRSRP of the reference antenna port group.That is, the UE performs reporting when a difference between pieces ofRSRP exceeds a specific threshold in an Adj_GRSRP ratio or dB scaleexpression as follows.

Adj_GRSRP(r,l,g)−Adj_GRSRP(r_0,1_0,m_0)>Threshold  [Equation 17]

Alternatively, as a modification of the proposed method, a UE specifiesreference RSRP through a current CSI-RS, compares RRM-RS-based RSRPresults with CSI-RS-based RSRP, and selects and reports the resultingRSRP.

RRM-RS for 3-Dimension (3-D)

The aforementioned method proposed according to an embodiment of thepresent invention may be modified and applied if the directivity of abeam is expanded from a 2-D space to a 3-D space. The directivity of abeam on the 3-D space is controlled by the two angles of a top/bottomangle (or vertical angle) and a left/right angle (or horizontal angle).Accordingly, in order to check whether an adjacent beam is present, itis efficient to index beams using two indices, that is, a horizontalindex and a vertical index. According to the characteristics of thepresent invention, in order for a beam index and an RRM-RS port index tohave a one-to-one correspondence relation, an RRM-RS port may be indexedwith a horizontal index and a vertical index.

In the case of a 3D MIMO system having M_v beams in the verticaldirection and M_h beams in the horizontal direction, a total of(M_v×M_h) beams are possible. In an embodiment of the present invention,an (M_v×M_h)-port RRM-RS is configured and a horizontal index j_h(j_h=0, M_h−1) and a vertical index j_v(j_v=0, M_v−1) are assigned toeach antenna port. One-dimension index i (i=0, M_v×M_h−1) and 2-Dindices j_h and j_v are assigned to each antenna port by taking intoconsideration the resource mapping of the (M_v×M_h)-port RRM-RS. Thereis a relation “(i)=f(j_h, j_v).”

FIG. 14 is a diagram illustrating antenna ports and antenna port groupsof RRM-RSs arrayed in 2-D indices according to an embodiment of thepresent invention.

Referring to FIG. 14, each of antenna ports is indexed with (j_h, j_v).If antenna ports are grouped every A_h×A_v ports by applying the methodproposed by an embodiment of the present invention and a port intervalbetween adjacent groups is set as B_h and B_v, an (i_h, i_v)-th portgroup includes RRM-RS ports (B_h×i_h+j_h, B_v×i_v+j_v), (j_h=0, A_h−1),(j_v=0, A_v−1). An eNB may designate the setting of the parameters A_h,A_v and B_h, B_v for a UE, or a UE may select the setting of theparameters by taking into consideration a channel environment and UEcapability and report the selected setting.

Difference Between RRM-RS and CSI-RS

In the existing LTE/LTE-A system, a CSI-RS is transmitted for thepurpose of a CSI report. A UE reports a RI, a PMI and/or CQI as CSI. Insome cases, the RRM-RS proposed by the present invention is used tomeasure RSRP for each antenna port. It may be better to use resources inwhich an existing CSI-RS can be configured rather than newly definingresources in which the RRM-RS is transmitted. The reason for this isthat transmission efficiency of legacy UEs is not deteriorated. If theRRM-RS is transmitted in a new resource, the legacy UEs do not recognizethe RRM-RS. As a result, transmission efficiency is deteriorated in asubframe in which the RRM-RS is transmitted or the RRM-RS is notscheduled. Accordingly, in a method for sending the RRM-RS usingresources in which the existing CSI-RS can be configured, a CSI-RSincluding a corresponding resource is configured in a legacy UE and thelegacy UE may be notified that data is not mapped to the correspondingresource.

Data is not mapped to a plurality of CSI-RSs configured in a UE for aCSI report. That is, a PDSCH is mapped to the plurality of CSI-RSs otherthan an RE to which the CSI-RS is mapped. In the proposed methodaccording to an embodiment of the present invention, as in the CSI-RS, aPDSCH may be mapped to the RRM-RS other than an RE to which the RRM-RSis mapped. In a modified method, however, a PDSCH may be mapped to theRRM-RS regardless of the RRM-RS. In this case, a UE needs to be able toreceive the RRM-RS and the PDSCH in the same RE at the same time.Alternatively, in order to guarantee the safe reception of the RRM-RS,an eNB may configure a corresponding resource as a ZP-CSI-RS so that aPDSCH is not mapped to the RRM-RS.

OCL Configuration of RRM-RS

If each cell sends an RRM-RS, the configuration of the RRM-RSstransmitted by a serving cell and neighboring cells may be designated toa UE. The UE measures a gain according to the beamforming of the servingcell and a gain according to the beamforming of the neighboring cells,and reports the measured gains to a network so that the gains are usedas a criterion for determining handover. The RRM-RS may be insufficientfor the tracking purpose of a signal because it has very lowtransmission density. Accordingly, tracking results are used to track asignal reliably received with high density, representatively, a CRS andto detect an RRM-RS. That is, the tracking results of the CRS of aserving cell are not suitable for being used for an RRM-RS transmittedby a neighboring cell due to an error in the oscillator which generatesthe carrier frequency of the serving cell and the neighboring cell.Accordingly, notification is provided of a quasi co-located (QCL) CRS(or another specific CS, such as a CSI-RS) that will be used to detectan RRM-RS for each RRM-RS. A UE uses the large-scale property propertiesof a channel, estimated from a QCL CRS (or another specific CS, such asa CSI-RS), to detect an RRM-RS. In this case, the large-scale propertiesof the channel may include one or more of delay spread, Doppler spread,a Doppler shift, an average gain, and average delay.

Extension to RSRQ

The proposed methods according to the embodiments of the presentinvention may be extended and applied to a method for measuring RSRQ foreach antenna port of an RRM-RS. RSRQ is defined as a ratio of RSRP andan RSSI. Accordingly, the measurement of RSSI is added. The measurementresource of the RSSI may be identically configured in all of RRM-RSshaving the same carrier frequency, that is, all of RRM-RSs configured inthe same component carrier. In this case, the results of a comparisonbetween the ports of RRM-RSs within the same component carrier are thesame although RSRP or RSRQ is used. However, a comparison between theports of RRM-RSs within heterogeneous same component carriers isdifferent depending on whether RSRP or RSRQ is used. Accordingly, an eNBdesignates whether RSRP or RSRQ will be used in a UE when the UEperforms an RRM report based on an RRM-RS.

In some cases, each RSSI measurement resource may be separatelyconfigured in an RRM-RS. In this case, a comparison between the ports ofRRM-RSs is different even within the same component carrier depending onwhether RSRP or RSRQ will be used. Accordingly, an eNB designateswhether RSRP or RSRQ will be used in a UE when the UE performs an RRMreport based on an RRM-RS.

Association Between RRM-RS RSRP and CRS RSRP

RSRP based on an RRM-RS according to an embodiment of the presentinvention has an object of incorporating the beamforming gain of an eNBhaving multiple antennas into the selection of a serving cell. Althougha specific neighboring cell has been determined to have the bestbeamforming based on the RSRP of an RRM-RS, if channels broadcasted by acorresponding cell, that is, a channel in which CRS-based demodulationis performed, is not stably received, the handover of a UE to thecorresponding neighboring cell cannot be performed. Accordingly, areport regarding whether both an RRM-RM and a CRS transmitted by aspecific eNB have better quality needs to be received from a UE, and ahandover determination and beam election need to be performed based onthe report. To this end, the UE reports RSRP of the j-th antenna port orport group of an i-th RRM-RS configured in the UE and also reports RSRPof a CRS connected to the i-th RRM-RS. In this case, the CRS connectedto the RRM-RS may be a CRS QCL-subjected to the RRM-RS.

A CSI measurement and reporting operation method of a UE for reducinglatency, which is proposed by this specification, is described below.

The method proposed by this specification may be extended and applied toan amorphous cell environment in addition to systems, such as 3D-MIMOand massive MIMO.

First, a 3D-MIMO system is described in brief below.

The 3D-MIMO system is one of the best transmission methods suitable forthe aforementioned single-cell adaptive antenna system (2D-AAS) eNB,such as that of FIG. 11, based on the LTE standard (Rel-12), and thefollowing operation may be taken into consideration.

As shown in FIG. 11, in the case of an example in which CSI-RS ports areconfigured from an 8-by-8 (8×8) antenna array, a total of verticallyprecoded 8-port CSI-RSs are configured/transmitted by configuringprecoded CSI-RS ports using “UE-dedicated beam coefficients” optimizedfor a specific target UE one by one with respect to every 8 antennasvertically.

Accordingly, a UE may perform conventional CSI feedback on 8 ports.

As a result, an eNB sends (precoded) CSI-RS 8 ports already applied to avertical direction beam gain, optimized for each UE (or specific UEgroup) to the UE.

Accordingly, since the UE measures a CSI-RS that has experienced a radiochannel, the UE can obtain a beam gain effect in the vertical directionof a radio channel through a CSI measurement and reporting operation onthe (vertically precoded) CSI-RS although it performs the same feedbackmethod based on a conventional horizontal direction codebook.

In this case, a method for determining a beam in a vertical directionoptimized for each UE includes (1) a method using RRM report resultsaccording to a (vertically precoded) small-cell discovery RS (DRS), (2)a method for receiving, by an eNB, a sounding RS (SRS) in the bestreception beam direction, converting the corresponding reception beamdirection into a DL-best beam direction based on channel reciprocity,and applying the DL-best beam direction.

If an eNB determines that a UE-dedicated best V-beam direction haschanged due to the mobility of the UE, in accordance with a conventionaloperation, the eNB reconfigures a CSI-RS and all of RRC configurationsrelated to an associated CSI process.

If an RRC reconfiguration process has to be performed as describedabove, latency (e.g., a unit of several tens of ˜several hundreds of ms)of an RRC level is inevitably generated.

That is, in the network dimension, a target V-beam direction ispreviously split into four, for example, and separate 8 port CSI-RSsthat have been precoded in respective V-directions are transmitted incorresponding separate transmission resource locations.

Furthermore, each UE has to perform CSI measurement and reporting on onespecific CSI-RS configuration of the 8 port CSI-RSs. Accordingly, whenthe target V-direction is changed, the UE has to perform an RRCreconfiguration procedure along with the network as a CSI-RSconfiguration to be changed.

Accordingly, a CSI measurement and reporting method for obviating orsignificantly reducing latency of an RRC level, which is proposed bythis specification, is described below.

That is, the method proposed by this specification relates to a methodof allocating only a single CSI process and a single uplink (UL)feedback resource to a UE and indicating which CSI-RS index (and/orCSI-IM index) is to be measured, that is, a target to be measured, inthe MAC level (or PHY level) other than the RRC level.

A MAC CE may be used for the MAC level indication, and DCI may be usedfor the PHY level indication.

That is, in the method proposed by this specification, an eNB (ornetwork) configures CSI-RS configurations for a plurality of candidateCSI-RSs in a UE using RRC signaling, and notifies the UE of “activation”indication explicitly or implicitly with respect to at least one CSI-RSthat belongs to the plurality of candidate CSI-RSs and on which CSI-RSmeasurement and reporting are performed.

For example, in the case where a CSI-RS 1 is an activated state, ifwhether a UE will move from the CSI-RS 1 to a CSI-RS 2 is taken intoconsideration, an eNB may first indicate “pre-activate” so that the UEcan previously track the CSI-RS 2 before the eNB issues a “re-activate”command that actually instructs the UE to move to the CSI-RS 2.

In this case, the tracking of the CSI-RS may mean an operation forperforming time and/or frequency synchronization on the CSI-RS so thatthe UE can measure the CSI-RS.

That is, a pre-activated CSI-RS x may be actually activated or notactivated (within a specific timer time).

In this case, the UE may receive an activation message indicative of theactivation of the CSI-RS x from the eNB and may feed full CSI reportingback to the eNB after a specific y ms.

In this case, the meaning that the full CSI reporting is fed back maymean that the UE performs meaningful CSI feedback to the eNB.

The CSI feedback may be determined to be meaningful or to be meaninglessdepending on the number of measured samples.

Capability Information Transmission

More specifically, in this specification, first, a UE notifies an eNB ofits capability information related to a CSI operation in advance (e.g.,upon initial access) by sending specific capability signaling to theeNB.

The capability information of UE related to a CSI operation may includeat least one of the following information.

In this case, the CSI-related operation may mean an operation related toa CSI-RS, CSI-IM and/or CSI process.

The writing of “A and/or B” may be interpreted as “at least one of A andB.”

1. Capability Information Regarding that how Many CSI-RSs (Nc inNumber), CSI-Interference Measurement (IM) (Ni in Number) and/or CSIProcesses (Np in Number) May be Subjected to “Full Activation” at theSame Time

In this case, the reason why the “full activation (configuration)” isexpressed is that an eNB can actually configure a total of Nc=threeCSI-RSs, Ni=3 CSI-IMs, and Np=4 CSI processes at the same time in thecase of a UE having Nc=3, Ni=3, and Np=4, for example. In this case, allof the CoMP operations in the conventional Rel-11 standard can besupported.

That is, this means that the UE has to perform channel measurement onall of the Nc=three CSI-RSs, perform interference measurement (IM) onall of the Ni=3 CSI-IMs, and perform CSI feedback on all of the Np=4 CSIprocesses.

2. Capability Information Regarding that how Many CSI-RSs (Nc′ inNumber), CSI-Interference Measurement (IM) (Ni′ in Number) and/or CSIProcesses (Np′ in Number) May be Subjected to “Partial Activation” atthe Same Time

In this case, the reason why the “partial activation” is expressed isthat only a specific partial operation (e.g., CSI-RS tracking) ofoperations which may be performed by a UE upon “full activation” islimited or a separate additional operation may be included.

For example, in a specific UE, parameters in 1. Capability informationmay be Nc=1, Ni=1, and Np=1 and parameters in 2. Capability informationmay be Nc′=3, Ni′=1, and Np′=1.

That is, there is only a difference of Nc=1 and Nc′=3.

This may mean that the specific UE maintains time/frequencysynchronization/tracking with respect to Nc′=3 partially activatedCSI-RSs and a CSI-RS that belongs to the Nc′=3 partially activatedCSI-RSs and that is subjected to a specific Nc=one “full activation” maybe designated to the specific UE.

Representative methods capable of designating the Nc=one CSI-RS include(1) a method of indicating a MAC CE command through the MAC layer and(2) a method for more dynamic indication in the PHY layer through DCIsignaling.

According to such a method, complexity and overhead for CSI feedback canbe always maintained identically because the UE has only to performsingle CSI feedback (in a specific CC) for one Np=Np′=one CSI process.

Furthermore, there is an advantage in that only a CSI-RS index to bemeasured by the UE can be dynamically switched through the signaling ofthe MAC layer or PHY layer using the method proposed by thisspecification.

That is, this specification provides a method for switching only aresource that is a target to be measured through RRC signaling, that is,signaling having latency smaller CSI-RS reconfiguration latency.

In this specification, for example, a CSI-RS is illustrated forconvenience of description, but it is evident that the method proposedby this specification may be extended and applied to the dynamicswitching of a CSI-IM index (or CSI process index) in the same manner.

In addition, there may be an additional restriction in the form ofNc<=Nc′, Ni<=Ni′ and/or Np<=Np′ between the parameters 1. Capabilityinformation and 2. Capability information.

In this case, the UE may send capability signaling only when such acondition is satisfied.

If an eNB receives capability signaling including capability informationof the UE related to a CSI operation from the UE, the eNB has to sendRRC signaling to the UE in a form that does not violate theaforementioned combination of capability characteristics when the eNBsubsequently configures the corresponding UE.

The UE does not expect a case where the capability characteristics areviolated and may consider the case where the capability characteristicsare violated to be an error case.

As described above, it is assumed that the eNB can configure all of thethree CSI-RSs corresponding to Nc′=3 in the UE through RRC signaling.

In this case, the UE may receive a separate identity capable ofidentifying that all of the three CSI-RSs are configured in a “partialactivation” state for each CSI-RS index or signaling capable ofrecognizing the separate identity based on specific implicit indicationfrom the eNB.

In this case, the UE performs time/frequency synchronization/tracking oneach of the three CSI-RSs from a point of time at which the RRCsignaling is received.

Synchronization/tracking may be performed based on information, such asa specific RS (e.g., CRS) that has quasi co-location (QCL) assumptionincluded in each CSI-RS configuration to be applied.

In this case, only a specific Nc=one CSI-RS of the Nc′=three CSI-RSs maybe additionally (or simultaneously) configured or indicated in theseparate identity form indicating that only the specific Nc=one CSI-RSis “full activation.”

Alternatively, the Nc=one CSI-RS may be implicitly previously defined asa specific index, such as that it is always defined as the lowest(highest) indexed CSI-RS.

Accordingly, the UE has only to perform channel measurement for CSIfeedback on the Nc=one “full activated” CSI-RS only.

That is, the UE performs only tracking on the remaining Nc′−Nc=twoCSI-RSs without performing channel measurement on the remainingNc′−Nc=two CSI-RSs.

As described above, in a method of performing channel measurement on theNc=one specific CSI-RS only and deriving feedback contents (e.g., aRI/PMI/CQI) through the measurement, an operation for calculatingfeedback contents for a specific CSI process configured along with theNc=one specific CSI-RS may be defined/configured.

For example, the UE receives a specific Np=one CSI process from the eNBthrough RRC signaling. The CSI process is defined as a combinationbetween a specific number of CSI-RSs and CSI-IM indices.

In this case, however, an operation for automatically incorporating afull activation CSI-RS depending on that a full activation Nc=one CSI-RSis which one so that it is recognized as a CSI-RS that is a target ofchannel measurement of a corresponding CSI process may bedefined/configured.

For another example, three CSI processes may be configured in a partialactivation state, for example, Np′=3, and the Nc′=3 CSI-RS indiceswithin the respective CSI processes may be configured.

Thereafter, the eNB may dynamically indicate an Np=one fullactivation-specific CSI process to the UE through MAC or PHY signaling.

Accordingly, the UE may send CSI feedback for the fullactivation-specific CSI process to the eNB.

As a result, a separate identity or a specific implicit signaling methodcapable of identifying whether a specific CSI-RS and/or CSI-IM indexindicated while operating in conjunction with the fullactivation-specific CSI process is a fixed index or an automaticallyvariable index for each specific CSI process as described above may bedefined in the specific CSI-RS and/or CSI-IM index.

If the specific CSI-RS and/or CSI-IM index has been fixed to a specificindex and indicated, the UE perform measurement on a resourcecorresponding to the fixed CSI-RS and/or CSI-IM index.

If the specific CSI-RS and/or CSI-IM index is set in a variable indexform and if a specific Nc=one CSI-RS is “full activation” throughseparate MAC or PHY signaling as described above, it may be applied in aform in which a corresponding index is automatically applied.

In this case, the full activation Nc may be two or more.

For example, the full activation Nc may be two or more if multipleCSI-RS resources in the 2D-AAS structure are together measured through aKronecker operation.

In this case, if what is the full activation Nc is separatelydynamically indicated, such indices may be automatically applied.

As a result, in such a CSI process configuration, a CSI-RS and/or CSI-IMindex which may be indicated in a corresponding configuration may beconfigured from which candidate set and may be defined from the RRCconfiguration step.

Likewise, it is evident that the configuration or indication operationmay be applied to the Ni′ and Ni number with respect to the CSI-IM.

FIG. 15 is a diagram illustrating an example of a CSI measurement andreporting method proposed by this specification.

Referring to FIG. 15, a UE sends capability signaling, includingcapability information of the UE related to a CSI operation, to an eNB(S1510).

The capability information of the UE includes first control informationindicative of a maximum number of CSI-related operations capable ofsimultaneously full activation and second control information indicativeof a maximum number of CSI-related operations capable of simultaneouslypartial activation.

Thereafter, when a configuration related to the CSI operation ischanged, the eNB sends CSI operation-related configuration information(or CSI-related operation configuration information) to the UE (S1520).

The CSI operation-related configuration information includes at leastone of partial activation CSI-related operation index informationindicative of a CSI-related operation for performing partial activationand full activation CSI-related operation index information indicativeof a CSI-related operation for performing full activation.

Thereafter, the UE measures a full activation CSI based on the CSIoperation-related configuration information (S1530).

Prior to the step S1530, the UE performs tracking on a partialactivation CSI-RS.

For a detailed description of the CSI-RS tracking, reference is made tothe aforementioned description.

Thereafter, the UE reports the measurement results to the eNB (S1540).

FIG. 16 is a diagram illustrating another example of a CSI measurementand reporting method proposed by this specification.

S1610 and S1620, S1640 and S1650 are the same as S1510 to S1540 of FIG.15, and thus a detailed description thereof is omitted.

After the step S1620 (after the eNB sends the CSI operation-relatedconfiguration information to the UE), the eNB sends an indicationmessage indicative of the measurement of a full activation CSI-RS to theUE (S1630).

The indication message may be a MAC CE or DCI.

Furthermore, the full activation CSI-RS may be selected from the partialactivation CSI-RS.

Point of Time at which CSI Measurement Window is Initialized/Updated

When a UE receives the full activation signaling of a specific CSI-RS,CSI-IM and/or CSI process index(s) from an eNB through MAC signaling orPHY signaling at a subframe (SF) #n point of time, the UE may apply CSImeasurement and reporting from a specific y ms since the correspondingpoint of time (i.e., the subframe #n), that is, from an SF #(n+y) pointof time.

In the case of periodic CSI reporting, the UE initiates CSI measurementand reporting for a specific CSI-RS, CSI-IM and/or CSI process index(s)that have been newly fully activated from a specific reference resourcepoint of time associated with an RI reporting instance that first comesout after the SF #(n+y) point of time.

That is, with respect to valid reference resource points of time presentin the SF #(n+y) point of time, CSI (e.g., an RI/PMI/CQI) calculated atthe reference resource point of time may be defined to report such newCSI contents from a point of time at which an RI is first reported.

This means that the UE does not perform reporting based on the newlyfully activated configuration although a PMI/CQI reporting instance ispresent prior to the first RI reporting point of time, but shouldcontinue to report CSI feedback contents based on a configuration rightbefore the newly fully activated configuration.

As a result, the UE performs CSI reporting based on a fully activatedconfiguration from a new RI reporting instance point of time.

In the above operations, configuration information related to a windowin which CSI measurement is averaged may also be defined to be providedseparately or together through RRC signaling.

Furthermore, such an operation may be defined with respect to only anenhanced UE that supports a configuration of a form, such as thefull/partial activation.

That is, conventional unrestricted observation is not performed, butmeasurement is averaged only within a specific [d1, d2] ms timeinterval.

The reason for this is that measurement averaging may be advantageouslydefined to be performed only within a specific bounded interval becauseresource configuration information for a CSI-RS and/or CSI-IM, that is,a target to be measured, may dynamically switch through MAC or PHYsignaling.

For example, if a UE receives signaling in which resource configurationinformation for a CSI-RS and/or CSI-IM, that is, a target to bemeasured, is dynamically switched/indicated through MAC or PHY signaling(e.g., by DCI) from an eNB, the UE may initialize or update ameasurement averaging window in which a CSI-RS-based channel is measuredwhile operating in conjunction with the signaling.

Furthermore, the UE may initialize or update the measurement averagingwindow in which corresponding CSI-IM-based interference is measuredwhile operating in conjunction with the (dynamically switched/indicated)signaling.

In this case, the meaning that the measurement averaging window isinitialized or updated means that the “start point of measurementwindow” called “from the random point of time” is initialized or updatedagain from a point of time #n (or after a point of time of a specificconfiguration/indication, e.g., #n+k) at which the (dynamicallyswitched/indicated) signaling is received, instead of a conventionaloperation for averaging channel measurement values from correspondingCSI-RS ports, repeatedly measured, for example, from the past randompoint of time to the current, by “unrestricted observation” for CSImeasurement according to the current standard according to a UEimplementation.

Alternatively, a method for explicitly signaling information about apoint of time regarding that a corresponding measurement window isinitialized or updated from which point of time through the signalingalong with (e.g., a timestamp form) may also be applied.

For example, there may be a method for indicating a time informationindication method for absolute time parameter values, such as an SFN anda slot number, or the signaling in a specific +/−Delta value form from apoint of time at which a UE receives the time information indicationmethod or the signaling.

In other words, the signaling may limitedly function to update/resetonly a point of time at which the measurement averaging window starts.

In this case, a UE may average CSI measurement values (depending on a UEimplementation) until additional signaling is received from acorresponding point of time.

The signaling may be separately (or independently) signaled for each CSIprocess. Accordingly, a measurement window reset may be independentlyapplied for each process.

The signaling may also be used to reset an interference measurementaveraging window for a specific CSI-IM resource.

In this case, the signaling also function to initialize a measurementaveraging window for a CSI-RS and CSI-IM belonging to a specific CSIprocess.

Alternatively, a method for signaling a separate (or independent)indicator for resetting an interference measurement averaging window fora CSI-IM resource may also be applied.

In this case, there is an advantage in that if there is a change in theinterference environment which may be predicted/sensed by an eNB, forexample, in an environment (e.g., eICIC, eIMTA or LAA) in whichinterference varies, the past interference environment is separated fromthe current point of time so that it is not incorporated into aninterference measurement value by notifying a UE that a measurementaveraging window for a specific CSI process is initialized.

FIG. 17 is a diagram illustrating yet another example of a CSImeasurement and reporting method proposed by this specification.

S1710 to S1730, S1750 and S1760 are the same as S1610 to S1630, S1640and S1650 of FIG. 16, and thus a detailed description thereof isomitted.

Referring to FIG. 17, after the step S1730, a UE initializes or updatesa CSI measurement window (S1740).

Thereafter, the UE repeatedly measures a full activation CSI-RS in aninitialized or updated CSI measurement window interval, averages themeasurement results, and reports an average value to an eNB(S1750˜S1760).

Prior to the step S1740, the eNB may send CSI measurement window-relatedconfiguration information to the UE.

In another embodiment of a form similar to the (dynamicallyswitched/indicated) signaling, in this specification, the aforementionedmeasurement window configuration-related operation may be applied to abeamformed CSI-RS-based method as follows.

For an elevation beamforming and FD-MIMO operation, the following PMIfeedback scenarios may be taken into consideration.

1. Precoding Definition for Elevation Beamforming (EBF)/FD-MIMO

(1) A Precoding Matrix/Vector

-   -   P₁: a wideband; less frequently updated    -   P₂: a subband or a wideband; more frequently updated    -   P is a function of P₁ and P₂, applied to a 1D or 2D antenna        array (P is a function of P₁ and P₂ applied to the 1D or 2D        antenna array.)    -   PMI(s) are to be specified w.r.t. The above definition

(2) Scenarios for CSI Feedback

-   -   1) Scenario 1    -   A UE measures CSI-RS ports beamformed with P₁(P₁ transparent to        UE).    -   PMI report(s) for P₂

2) Scenario 2

-   -   A UE measures non-precoded 1-D or 2-D CSI-RS ports

Note: P₁ not applied to a CSI-RS at an eNB

-   -   A PMI report(s) for P₁ and P₂

3) Scenario 3

-   -   A UE measures both non-precoded 1- or 2-D CSI-RS ports (lower        duty cycle) and a CSI-RS beamformed with P₁    -   A PMI report(s) for P₁ and P₂

4) Scenario 4

-   -   A UE measures non-precoded 1- or 2-D CSI-RS ports

Note: P₁ not applied to a CSI-RS at an eNB (P₁ indicated to UE).

-   -   PMI report(s) for P₂

For example, in a method using a beamformed CSI-RS, such as thescenarios 1 and 3 of the scenarios 1 to 4, if a matrix P1 in whichbeamforming has been applied to corresponding CSI-RS ports by an eNB ischanged although a UE does not need to know the matrix P1 itself, theeNB needs to previously notify the UE of information related to a pointof time at which the matrix P1 was changed.

Accordingly, the UE may configure/apply a proper measurement averagingwindow when measuring and calculating CSI.

That is, according to the current standard, when a UE performs channelmeasurement on corresponding CSI-RS ports, the UE averages channelmeasurement values from corresponding CSI-RS ports, repeatedly measuredfrom the past random point of time to the current, by “unrestrictedobservation” according to a UE implementation, thereby being capable ofimproving reliability (e.g., a noise suppression effect).

In the scenarios 1 to 4, however, since beamformed CSI-RS ports notknown to the UE are used in the matrix P1 itself, the eNB may change thematrix P1 at a random point of time. If the eNB does not notify the UEthat the matrix P1 has changed, the UE can average the channelmeasurement values of the matrix P1 prior to the change and a matrix P1′after the change. Accordingly, there may be generated a problem in theaccuracy of corresponding CSI measurement and reporting.

Accordingly, in order to solve such a problem, this specificationproposes a method for sending, by an eNB, a kind of “beam-changenotification” or “beam-change indicator (BCI) signaling” to a UE.

A “beam-change indicator” is hereinafter simply called a “BCI.”

The BCI signaling may be indicated in an RRC signaling form.

However, the BCI signaling may be provided as signaling through a MAC CEor dynamic indication through a DCI.

In other words, when a UE receives BCI signaling from an eNB, the UEupdates the start point of a measurement averaging window applied whenCSI is derived in a corresponding CSI process with a point of time atwhich corresponding BCI signaling is received (or a point of timespecifically indicated from the point of time at which the correspondingBCI signaling is received or a point of time explicitly indicated by aseparate timestamp).

That is, a method for explicitly signaling information (e.g., atimestamp form) about a point of time regarding that a correspondingmeasurement window is initialized or updated from which point of timealong with BCI information (or as associated information) may also beapplied.

For example, the method may include a method for indicating timeinformation about absolute time parameter values, such as an SFN and aslot number, or a method for indicating, by a UE, the signaling in aspecific +/−Delta value form from a point of time at which the signalingis received.

In other words, such BCI signaling may be limited to the role ofupdating/resetting only the start point of time of a measurementaveraging window.

In this case, the UE may average CSI measurement values (depending on aUE implementation) from the point of time (i.e., the point of time atwhich the BCI signaling is received) to a point of time at whichadditional BCI is received.

As a result, the UE does not know the updated matrix P1 itself, but hasbeen notified that the matrix P1 has been updated through the BCI.Accordingly, the UE can perform CSI calculation and reporting (e.g., thematrix P1, P2, RI and CQI) for a corresponding CSI process with respectto only CSI-RS ports to which the updated matrix P1 has been applied bynewly averaging CSI measurement values from the point of time.

The BCI may be separately (or independently) signaled for each CSIprocess.

Accordingly, a measurement window reset can be independently applied foreach process.

The BCI may also be applied to reset an interference measurementaveraging window for a specific CSI-IM resource.

In this case, the BCI also functions to reset a measurement averagingwindow for a CSI-RS and CSI-IM belonging to a specific CSI process.

Alternatively, a method for signaling a separate (or independent)indicator for resetting an interference measurement averaging window fora CSI-IM resource may also be applied.

In this case, there is an advantage in that the past interferenceenvironment can be separated so that it is no longer incorporated intoan interference measurement value from a current point of time bynotifying a UE that a measurement averaging window for a specific CSIprocess has to be reset if there is a change in an interferenceenvironment that may be predicted/sensed by an eNB, for example, in anenvironment (e.g., eICIC, eIMTA and LAA) in which a change of aninterference environment is present.

General Apparatus to which an Embodiment of the Present Invention May beApplied

FIG. 18 is a block diagram of a wireless communication apparatusaccording to an embodiment of the present invention.

Referring to FIG. 18, the wireless communication system includes an eNB1810 and a plurality of UEs 1820 located in the area of the eNB 1810.

The eNB 1810 includes a processor 1811, memory 1812, and a radiofrequency (RF) unit 1813. The processor 1811 implements the functions,processes and/or methods proposed in FIGS. 1 to 17. The layers of aradio interface protocol may be implemented by the processor 1811. Thememory 1812 is connected to the processor 1811 and stores various typesof information for driving the processor 1811. The RF unit 1813 isconnected to the processor 1811 and sends and/or receives a radiosignal.

The UE 1820 includes a processor 1821, memory 1822 and an RF unit 1823.The processor 1821 implements the functions, processes and/or methodsproposed in FIGS. 1 to 17. The layers of a radio interface protocol maybe implemented by the processor 1821. The memory 1822 is connected tothe processor 1821 and stores various types of information for drivingthe processor 1821. The RF unit 1823 is connected to the processor 1821and sends and/or receives a radio signal.

The memory 1812, 1822 may be located inside or outside the processor1811, 1821 and may be connected to the processor 1811, 1821 by variouswell-known means. Furthermore, the eNB 1810 and/or UE 1820 may have asingle antenna or multiple antennas.

In the aforementioned embodiments, the elements and characteristics ofthe present invention have been combined in specific forms. Each of theelements or characteristics should be considered to be optional unlessotherwise described explicitly. Each of the elements or characteristicsmay be implemented without being combined with other elements orcharacteristics. Furthermore, some of the elements and/or thecharacteristics may be combined to form an embodiment of the presentinvention. The sequence of the operations described in connection withthe embodiments of the present invention may be changed. Some ofelements or characteristics in an embodiment may be included in anotherembodiment or may be replaced with corresponding elements orcharacteristics in another embodiment. It is evident that in the claims,claims not having an explicit citation relation may be combined to formone or more embodiments or may be included as one or more new claims byamendments after filing an application.

An embodiment of the present invention may be implemented by variousmeans, for example, hardware, firmware, software or a combination ofthem. In the case of implementations by hardware, an embodiment of thepresent invention may be implemented using one or moreapplication-specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers and/ormicroprocessors.

In the case of an implementation by firmware or software, an embodimentof the present invention may be implemented in the form of a module,procedure, or function for performing the aforementioned functions oroperations. Software code may be stored in memory and driven by aprocessor. The memory may be located inside or outside the processor,and may exchange data with the processor through a variety of knownmeans.

It is evident to those skilled in the art that the present invention maybe materialized in other specific forms without departing from theessential characteristics of the present invention. Accordingly, thedetailed description should not be construed as being limitative fromall aspects, but should be construed as being illustrative. The scope ofthe present invention should be determined by reasonable analysis of theattached claims, and all changes within the equivalent range of thepresent invention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

The method for feeding back CSI in a wireless communication systemaccording to an embodiment of the present invention has been illustratedbased on an example in which the method is applied to the 3GPP LTE/LTE-Asystems, but may be applied to various wireless communication systems inaddition o the 3GPP LTE/LTE-A systems.

1. A method for reporting channel state information (CSI) in a wirelesscommunication system, the method performed by a user equipment (UE) andcomprising: receiving, from an evolved Node B (eNB), radio resourcecontrol (RRC) signaling including channel state information-referencesignal (CSI-RS) configuration information for a CSI reporting operationcontrolling activation of a CSI-RS resource by a medium access control(MAC) control element (CE), wherein the CSI-RS configuration informationincludes information for a plurality of CSI-RS resources; receiving,from the eNB, a MAC CE command including control information indicatingwhether to activate at least one CSI-RS resource among the plurality ofCSI-RS resources; measuring channel state using a CSI-RS transmittedthrough at least one activated CSI-RS resource among one or moreactivated CSI-RS resources for which activation is indicated by thereceived control information; and reporting the measured channel stateinformation to the eNB.
 2. The method of claim 1, wherein the at leastone activated CSI-RS resource is a specific CSI-RS resource, the methodfurther comprising: receiving, from the eNB, indication informationindicating the specific CSI-RS resource among the one or more activatedCSI-RS resources.
 3. The method of claim 2, wherein the indicationinformation is included in downlink control information (DCI).
 4. Themethod of claim 1, wherein the control information is received in asubframe #n, wherein the one or more activated CSI-RS resources forwhich activation is indicated by the control information is applied in asubframe #n+y, and wherein the subframe #n+y is a subframe after the ythsubframe from the subframe #n.
 5. The method of claim 1, furthercomprising: transmitting capability information of the UE to the eNB,wherein the capability information of the UE includes informationrelated to a maximum number of a specific CSI-RS resource supported bythe UE. 6-8. (canceled)
 9. The method of claim 1, further comprising:receiving information related to a CSI-RS measurement window from theeNB, wherein the measuring channel state using the CSI-RS comprising:initializing or updating the CSI-RS measurement window when the MAC CEcommand is received; repeatedly performing the measurement of a CSI-RSfrom a point of time at which the CSI-RS measurement window isinitialized or updated to a specific period; and averaging the measuredresults.
 10. The method of claim 9, wherein if the CSI reportingoperation is a periodic CSI reporting, the point of time at which theCSI-RS measurement window is initialized or updated is a specificreference resource point of time related to a rank indicator (RI) reportfirst generated after the specific period.
 11. The method of claim 1,wherein the MAC CE command is received from the eNB for each CSIprocess.
 12. (canceled)
 13. A user equipment for reporting channel stateinformation (CSI) in a wireless communication system, the UE comprising:a radio frequency (RF) unit sending or receiving a radio signal; and aprocessor controlling the RF unit, wherein the processor is configuredto: receive, from an evolved Node B (eNB), radio resource control (RRC)signaling including channel state information-reference signal (CSI-RS)configuration information for a CSI reporting operation controllingactivation of a CSI-RS resource by a medium access control (MAC) controlelement (CE), wherein the CSI-RS configuration information includesinformation for a plurality of CSI-RS resources; receive, from the eNB,a MAC CE command including control information indicating whether toactivate at least one CSI-RS resource among the plurality of CSI-RSresources; measure channel state using a CSI-RS transmitted through atleast one activated CSI-RS resource among one or more activated CSI-RSresources for which activation is indicated by the received controlinformation; and report the measured channel state information to theeNB.
 14. The UE of claim 13, wherein the at least one activated CSI-RSresource is a specific CSI-RS resource, wherein the processor isconfigured to receive, from the eNB, indication information indicatingthe specific CSI-RS resource among the one or more activated CSI-RSresources.
 15. The UE of claim 14, wherein the indication information isincluded in downlink control information (DCI).
 16. The UE of claim 13,wherein the control information is received in a subframe #n, whereinthe one or more activated CSI-RS resources for which activation isindicated by the control information is applied in a subframe #n+y, andwherein the subframe #n+y is a subframe after the yth subframe from thesubframe #n.
 17. The UE of claim 13, wherein the processor is configuredto: transmit capability information of the UE to the eNB, wherein thecapability information of the UE includes information related to amaximum number of a CSI-RS resource supported by the UE.